I know on the Tested forum there are a lot of people building PCs for BF3. While mine was built in preparation for BF3, I play just about every game that comes out, so it's not exclusively for BF3. I dropped about $2100 building this mammoth and can't wait to finally give it a challenge (even The Witcher 2 on maximum everything doesn't get it going).
If you did, what did you build? For me:
Core i5 2500k overclocked to 4.0Ghz, Two GeForce 570 GTXs in SLI, 8GB DDR3, 128GB SSD, 2TB HDD
Should be able to play BF3 at maximum options with ease. The alpha certainly offered no real stress. Downloading the beta now.
Just curious what everyone else will be rocking.