My anecdote...
I tend to upgrade to whatever's the best or second best graphics card available at the time. After giving up on Mac gaming in 2002, I built my first PC with a Radeon 9700 Pro. That card lasted me three years, an eternity, because Nvidia dropped the ball hard with the GeForce FX 5000 series. The GeForce 6000 series was definitely an improvement, but I was in no hurry at the time to upgrade.
I moved to a GeForce 7800 GT + Athlon X2 3800+ in 2005 when my 9700 Pro + Pentium 4 2.4B were no longer cutting it in WoW. The 256MB 7800 GT compared favorably with the 256MB X1800 XL, so it was a coinflip.
After that I went with an HD 3870, then a GTX 260 Core216. The GTX 260 was a bit much and it would overheat in games where the shaders were allowed to go full bore. The card hit the mid-90C range and would lock up my PC, so I sidegraded to an HD 4890. Because the next generation of ATI was so good, I bought an HD 5870. I had originally planned to upgrade after a year, but neither the HD 6000 series or GTX 500 series blew me away.
And now I have an HD 7970. This wasn't really an upgrade out of necessity, but because the market for used HD 5870s is surreal (thanks Bitcoins.) I sold mine for $200 and put it toward the new card. Admittedly the HD 7970 does not blow the GTX 580 out of the water. In fact, I hate the reference coolers on the AMD cards vs. Nvidia's. I bought the card because I didn't feel like waiting anymore. Had Nvidia released an equivalent GPU at the same time, I very well may have bought that instead.
The problem with Kepler for me? It's literally vaporware right now. There simply was not any concrete info about the product for me to justify waiting a bit longer. If the high end Kepler part proves to be a massive jump in performance, I will gladly sell my HD 7970 on CL or eBay for one.
For me it came down to timing.