Been mining for a few days only, since the recent media articles on bitcoin.
My Nvidia 8800GTX was the shit 4 years ago, at $500-600, but it mines at only 26 MH/s, miner software are optimized only for Radeon's stream processors, not Nvidia CUDA.

I was planning to build a new PC later this year, might as well do it now, using Radeon cards this time.
I'd love to use 2-3 6990s but they are out of stock, so I'll aim for 1 GH/s instead of 2.