If my math is correct, Deepbit mines about 2,556BTC per day on average. If I were Deepbit, and I wanted to cash out on the 5,000Gh/s+ I had:
Deepbit is a pool. The bitcoins they mine aren't theirs. They can't sell them.
I am truly curious about this because I might someday be in possession of that many BTC and want to know any negative consequences of selling off.
Since people would have to buy bitcoins to give them to you, there would likely be no significant net negative consequences. In fact, the more things people can buy with bitcoins, the more bitcoins stay in circulation rather than getting cashed out.