The problem with fanboyism is it encourages people to buy inferior products or spend more for the same performance solely because of brand name. When I was building my rig last December, the 6850 was $30 cheaper than the 1GB 460, performs better and runs cooler and quieter.
As for the drivers, I'm with reflex. I haven't had any driver problems to date (and I hope I haven't jinxed it). You really run into issues once you start CF and multi-screen setup.
The thing about SLI/CF versus one card is pretty complicated. Some people claim that micro-stuttering and games that won't be supported means it's worthless. You'll also most likely have to buy a better PSU, mobo and possibly case. You will still see a difference though. CF 6850s scale at about 80-90%. That means adding that second card yields almost double the increase (which is pretty damn good).
And, if you are looking into SLI/CF, I would suggest buying lower-end new cards instead of older high-end cards. Even though right now 2x4870s is technically better than a 560, the 560 supports DX11 and has great tessellation.
