This is a question that has been on my mind for a while. I was going to buy a server farm to mine Bitcoins and I was wondering if it would be practical to jump on the mining bandwagon at the current time.
If you want to calculate your farm's profitability, you can use various online calculators to do that, like mine for example. You should take into consideration such scenarios as the reward for blocks halving soon, difficulty increasing, price going down and so forth and see whether or not it's worth your investment.
Generally, GPU mining might not be the best choice at the moment, its profit margins are narrow. FPGA miners are more effective, but are generally pretty costly at the start. The new trend appears to be ASIC miners which can also be quite costly but are extremely good at mining.