Nope. Not selling a single GPU / rig. There will be another *boom* one of these days.
History tends to repeat itself. I'll be ready this time
I'm also holding on to some, but by the time that happens (if..) our top end GPUs might not be worth it anymore.
See though, i have a bunch of 7950s / 270s. Their power/hash ratio won't be the best, but they won't be the worst either. The new round of AMD cards will likely mirror the current crop of Nvidia Kepler GPUs in hash/watt (or do better) so efficiency is definitely better, but the 7950s and 270s were both at least 3khs / watt at a very bad minimum. You can still make cash on that.
Now, all of that said, i probably should have sold my farm earlier this year when 7950s were going for $400+. We may or may not see that again, but when GPU mining does kick back up, i'll have a decision to make for sure because i fully expect people to do the same exact thing they did this summer which was get cards at any cost.
If the next gen cards are the right price / available and people are paying up for the old cards, then dump my current farm and swap out for new cards. Else, hold on to current farm and mine.