Re: 2x GTX 460 1GB in SLI vs. GTX 480
SLi is a lot better than it was years ago. Most games work pretty well with SLi although there is the occassional game that does not work with it. In cases like this though you can still use SLi AA so you can at least get better image quality in games with SLi issues.
I would choose 2 460's over a GTX 480 any day.