True, but bitfromit was not referring mistakenly to 5% in the quoted text -- but rather in my previous reply. If you check the details for the TAT version of the passthrough, you'll find:

"Each TAT.ASICMINER share has the right to 95% of its respective dividends. 5% will be retained for asset management fees."

https://btct.co/security/TAT.ASICMINER

On TAT's own exchange, the fee is the same.

If you first get the canonical Bitcoin daemon running, you can then interact with it via PHP. The main Bitcoin wiki includes a page specifically for PHP developers here:

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

No need to reinvent the wheel. 

Another UK service which I've used myself is speedybitcoin.co.uk. As I mentioned in a separate thread (https://bitcointalk.org/index.php?topic=247083.msg2625605), you specify a receiving address, and whenever you send a bank transfer using particular details, you receive Bitcoins at that address based upon the current Mt Gox exchange rate. Note, though, that Mt Gox prices have been out of whack since their announcement that USD withdrawals would be temporarily suspended for two weeks as of 20 June. If you give it a few days, hopefully the rate there will settle toward something closer to what it is everywhere else.

Note that the version of passthrough shares which trade on Havelock -- which was set up by ThickAsThieves (TAT) last month -- charges a 5% fee against dividends. The TAT passthrough fund on BTCT.co charges the same. By comparison, the PT shares offered by burnside on BTCT.co do not currently charge a fee against dividends. If you'd like to receive the full dividend, the TAT version of the passthrough is best avoided.

There's a useful profitability calculator available here:

http://www.bitcoinx.com/profit/

Unfortunately, in the site's own words, "Extrapolating bitcoin difficulty or price is pure voodoo", and estimating return on investment requires an estimate of both. If all the ASIC vendors promising delivery "real soon now" actually do deliver, the current total network hashing power will soon look pretty pedestrian, and the return from mining for a given level of power will fall sharply. For example, you can see a list of impending hashing power just for BFL in an entirely unofficial list here:

http://bfl.ptz.ro

PT shares for ASICMINER are also available on Bitfunder.

The ASICMINER website is at asicminer.co, while Friedcat's main ASICMINER thread on the forum is here:

https://bitcointalk.org/index.php?topic=99497.0

As far as I can tell, there doesn't seem to be a dedicated news source just for ASICMINER, so you'll have to wade through quite a bit of third party commentary on the bitcointalk.org thread.

A lighter weight client such as Multibit can provide a local wallet without storing the entire contents of the blockchain:

http://multibit.org

Although you won't get the warm fuzzies that come from fully supporting the computational overhead of the Bitcoin network, opting for a lightweight client does mean a much smaller storage space -- a few megabytes -- and a much lower requirement for raw computing power.

You didn't mention where you're geographically located, but for UK users, I've found the service at speedybitcoin.co.uk to be very quick and reliable. You specify a receiving address, and whenever you send a bank transfer using particular details, you receive Bitcoins at that address based upon whatever the current Mt Gox exchange rate might be, less a commission. If you write and ask for a 'tailored account', you can get the commission reduced and the daily limits increased without a problem.

One caveat: since Mt Gox prices have been out of whack since their announcement that USD withdrawals would be temporarily suspended for two weeks as of 20 June, I wouldn't necessarily use any service just yet that relies on automatic quotes from Mt Gox.

Yes, the Mt Gox USD/BTC has been out of whack since they announced a two-week temporary closure of the USD withdrawal facility on 20 June -- artificially increasing the USD-based demand for BTC, which faces no such restrictions.

As for arbitrage between exchanges, Seal had a pretty good go at it via an automated bot, with reportedly great results:

https://bitcointalk.org/index.php?topic=114351.0

I think the opportunities in this space have been reduced somewhat by auto-routing to the best price exchange, such as that available on Bitfinex, but no doubt if there's still money to be made via inter-exchange arbitrage, someone will do it. In my view, though, it would not be remotely worth a human's time to do it manually, when machines can do it so much more efficiently.

Just to add -- in case the OP might have been wondering about the private key corresponding to an address, which does have a few uses, such as moving from one type of wallet to another -- the private key corresponding to a given address can be extracted from the Bitcoin-Qt client with the console command dumpprivkey followed by the address whose key you're extracting. (The console is available via the 'Debug' window.) The MultiBit client makes this a little easier, with an export function right on the 'Tools' menu.

If you're ever wanting to use the underlying private keys to move from one type of wallet to another, though, you'll need to be fanatically cautious about the hidden change addresses which the clients use to receive change from outgoing transactions. It's entirely possible to copy a slew of private keys, one for each of the receiving addresses you have created, from one client to another, confirm that all the outgoing transactions show up in the new client, and then discover that -- oops -- your balance is lower than it ought to be. (To make matters worse, different clients handle addresses for transaction change in different ways.)