millicoin informally.

If I was pricing something in print I would just use mBTC.

I was asking the OP.  I believe his argument is flawed.  I agree with you in that IF there is a conflict of interest it is that panic/volatility/chaos leads to higher volume = more trading fees.

Which is greater?
1% * 200,000 * $120
1% * 400,000 * $60

Shows a complete lack of understanding on how Bitcoin (or more generally crypto-currencies work).  One can't "peg" anything without centralized control.  If you have centralized control you have no need for the overhead of the blockchain and you now must have implicit trust in the issuer/controller.

The QR code contains the shared secret (which is what synchronizes the codes on your smartphone and the site's backend server.  Same shared secret + same time means both you and site generate the same code in sync.   The shared secret is simply a number.  The QR code also contains some less important information like "display name".

So if you have a backup of the QR code you use it to "setup" another smartphone

1) When you setup 2FA before you scan the QR code print it out.  
2) Instead of scanning the QR code on screen scan the printout (this verifies the printout was correct, no printing errors rending it unreadable).  
3) Complete the 2FA setup.
4) Now just label the printout.
5) Store the all your labeled google authenticator QR codes in a safe place (like fireproof safe or safety deposit box).

Exactly.  If an acre of this hypothetical land nets $250 per year in rent, then the present value (i.e. purchase price) is something like 20x annual rent cashflow or $5K per acre.  100 acres @ $5K ea = $5M.  If you have $5M in performing assets the reality is you likely don't need to work.  Land isn't special in that respect.

Of course once you redistribute land them people will store more of their wealth in other assets.  So what is next?  Free stocks & bonds for the average person?

The least efficient miners will quit, difficulty will lower and eventually a new equilibrium will exist.

No that has nothing to do with this.  One could still "embed" data in the blockchain by just ensuring the outputs are larger than the dust threshold.   

Exactly.  If one lived on a lunar colony or orbital station one better believe someone would be charging for air.  Maybe it would be rolled in with your rent, maybe it would be simplified to a standard fee per person but air would be scarce and the delivery of air a service.

I think you misunderstand.  Nobody is saying the blockchain can't be pruned.  IT CAN be pruned however the UXTO (set of unspent outputs which can still be inputs for future txs) CAN'T be pruned.  That is fine because generally the UXTO is going to grow slower than the blockchain (people tend to spend unspent outputs creating roughly the same number of unspent outputs).  There is one exception.  That is UNECONOMICAL outputs.

If you have a 0.0000001 output but it would cost 100x as much in fees to spend it would you spend it?  Of course not.  Kinda like mailing a penny (at a cost of $0.46) to your bank to apply to your mortgage principal.  Nobody does that it doesn't make economical sense.  So these uneconomically outputs are likely NEVER going to be spent.  Each one that is produced won't be spent and thus won't be pruned and will remain in the UXTO forever (or a very long time on average) this is causing the UXTO to bloat and will continue to bloat as there is no reason for anyone to ever spend these outputs (and spending is what allows an output to be pruned).

The UXTO is the critical resources.  In order to validate tx quickly the UXTO needs to be in memory.  So what happens when the UXTO is 32GB? 64GB? 200GB?  Now if those are "valid" outputs likely to be used in future tx well that is just the cost of being a full node.  But when 50%, 70%, 95%+ of the outputs are just unspendable garbage it greatly increases the processing requirements of full nodes without any benefit, to anyone.

Of course you don't which is the whole point of pruning the blockchain however you do need to retain a copy of every unspent output otherwise when you receive tx or block containing that output as an input in a new tx you can't validate the tx or block.  If the input is coming to you, you can't even know if the tx/block is valid or just some nonsense garbage that an attacker sent to trick you into thinking your got paid.

This unprunable dataset is a subset of the blockchain however tx below the dust thresholding simply bloat this.

No.  Data directory (folder) is in a different location.  Depends on your OS

https://en.bitcoin.it/wiki/Data_directory

Even if a client doesn't check, the protocol requires that a tx have valid addresses otherwise the tx is invalid.

Note there is a difference between invalid address and a valid one in which the private key is lost/unknown (or was never known).

$110 +/- $20.

Double check you have a backup of the wallet.dat file.  Ensure the client is closed, then delete the wallet.dat in the bitcoin datadir.  Restart the bitcoin client and it will produce a new wallet.dat.  Right away BEFORE DOING ANYTHING ELSE
a) encrypt the wallet
b) ensure you can decrypt the wallet
c) make an offline backup of the passphrase
d) make a backup of the encrypted wallet.dat file

Then you have to implicitly trust the entity making checkpoints.  Say you are a new user and you download the latest version of the client and it has a checkpoint for block 200,000 which says I have 100 BTC.  Prove that I do or don't legitimately have 100 BTC without any information prior to block 200,000.  What a developer owes me a lot of money so I say "you can pay your debt by putting a fake balance into the checkpoint for me".  There is no longer Satoshi's goal of commerce without a trusted third party. 

Remember the point of the blockchain is to decentralize verification and validation.  Any node, running any version of the client produced by anyone given a copy of the genesis block can prove every block and thus every current "balance" is valid.

So block 123,456 shows I (or more correctly an address I have) have a balance of 100 BTC.  How do you verify it?  If all you have is the balance how do you know it is correct?  If you can solve that problem then you can build a more efficient

Hint: miners might actually be attackers, scammers, thieves, etc.  In Bitcoin miners can't falsify coin records.  If they make a block which shows a "fake transaction" other nodes (which inherently DONT TRUST any other node) can verify the block is invalid a reject it.  How can they do that?  Because they can trace the history of every coin and thus can prove a tx is valid.

Don't start by thinking of how "X" would work.  Start by thinking of how someone could abuse/attack/defraud "X".  Remember this is money we are talking about here.

blerg.  I should have known.  Amazon lost their tax fight in VA last year.  Still I think this year passage is unlikely.  If it was an intrade bet with even money I would bet against it.  Now looking out over the next 5 to 10 years ... well the prospects of keeping it at bay are looking more dim.

... and end up -$50 to -$100 after chargebacks.

Any restriction on PayPal is defacto a restriction on ebay as you MUST accept PayPal as a condition of listing on ebay.  Just because ebay doesn't kill every listing within seconds doesn't mean they support it.  There are something like 20 million auctions on ebay at any particular time.  It simply isn't cost effective to monitor them all continually.

It would be like a cop stops you for speeding 75 in a 60.  You say to the cop "if speeding is illegal then why didn't someone stop me yesterday when I was speeding?  Obviously you must be incorrect and speeding is not illegal" 

Sorry typo was trying to say a quadrillion quadrillion (i.e 10^15 * 10^15).  Still the point is that 2^256 is "big".  Deceptively big since for example we have 64 bit computers and some people even have 32 bit dollars (~$4.3 billion USD) so at a "common sense" level it doesn't seem like the jump to 128 bit or 256 is "that much more".