Well, I'm still not in "post 3.5" world yet, still running a campaign in it. I don't see a "post 4e" world either, unless they turn off 4e DDI. I don't need to buy new product to run or play in games, my 4e games will continue along nicely.
Lots of good games out there. When one of my current games ends, I'll probably push to try something new. Currently 13th Age, Marvel Heroic Roleplay, D&D Next, and Dresden Files are looking promising. (Could also do something else Fate besides Dresden.) Though one of my top five favorite DMs may start up an Eberron game in 2013, and he'd probably want to run it in some edition of D&D.
Really, there's so many good games out there, the question is "what will you have time for next". A word of advice - if all you've played is D&D, give some other systems a try, especially some modern indie games. I'm not saying they are better than D&D, but I will say that they are likely different than D&D. There's no "right" system for all situations. There's the system(s) that are "right" for what you and the others in your group want to play next.
Lots of good games, go forth and enjoy!