Also, you should factor in that in the winter you need to heat your house anyway, so the waste heat from your computer helps offset your other heating bills.  In the summer in warm climates, this has the opposite effect.  You can end up paying electric rates to run the computer, and then even more electricity for air conditioning.

I have invested in the Second Life world since 2006, and became a very active currency trader there. It was not the "price speculation" type of trading, but rather arbitrage by offering to buy and sell their internal currency from other users.  The margins were small (0.4% per trade), but steady.  As long as I could trade in enough monthly volume, it made a reasonable investment.

My philosophy on cashing out was simple: I took money out when I needed it, or when the returns became lower than alternative investments.  The latter happened in Sept of this year, so I have cashed out all but a residual amount.

For those not familiar, Second Life is a virtual world with a very active internal market.  Their currency exchanges transact US$ 350,000 per day.  The internal currency, the Linden Dollar (L$), is issued by the owners of the World, mostly as a weekly stipend to users with a premium account.  Users can exchange the currency without overhead with each other, for any reason.  Most of it goes to paying for virtual land in the world, and buying items to wear or use for your avatar.  The exchanges allow you to cash out your L$ to other currencies, including bitcoins via Virwox.

For Bitcoin, for now I am just accumulating a balance, via mining and gradually exchanging my residual balance through Virwox (I still get weekly stipends from my premium accounts, until the subscriptions run out).  I have not yet found a niche to earn coins by selling a product or service, and the amount of BTC is not very large, so my strategy for now is just buy and hold, and see how Bitcoin develops.  Just watching governments and banks inability to understand Bitcoins has been sufficient entertainment, and the mining helps heat my house in the winter, so I feel like I have got enough value out of them to not worry about getting a profit.

In economics, "Velocity" is the number of times a currency is used per year.  It's total transactions in an economy divided by the money supply.  For example, if the United States GDP is $15 trillion, and the money supply is $2 trillion, then the velocity is 7.5 per year.

My question is has anyone calculated or charted the bitcoin velocity?  I think it could be found by summing the transactions in blocks, but that might be a naive assumption.

Why it might be interesting is as a measure of "are people spending or sitting on coins?" relative to other currencies.

EDIT: I found bitcoinwatch.com, and it shows 538,000 coins sent in the last 24 hours, which implies a velocity of 29 per year.  What is not obvious is how many of those coins were simply moving from one account to another of the same owner, which would not be an "economic transaction", any more than pulling cash from an ATM against your checking account is. 

Why would Tycho limit his own income?  He gets 3% of the pool, so bigger is better I would assume.