Are you guys not doing it because of the initial cost for building GPU rigs or because of the looming threat of ASIC? I made my first two rigs last month, one with four 7950s and one with two 5970s. They've been pumping out about 4gh/s and I've made about 4 BTC. Subtract the cost of electricity and one of the 7950s has paid for itself already. I also didn't have all the cards up and running on the same day, more like a week in between the first and last two 7950s. I expect this month to be a little better.