padgettl -- AFIK, Epson has fixed all but the noisy iris (as noted in the other posts on this page, and the recent ones) on the 6500UB/7500UB. The 8500UB won't be available for at least several months (November/December time frame is my estimate - Jason Turk should have better info though).
Remember that any new PJ may well have teething pains. If you are really itching to get a PJ, the 6500UB is your best bet. Yes the new models should be better. However, if you want it for watching HDTV & sports (with an occasional movie, once or twice a week), and want some ambient light in the room, then the new models won't give you any real improvement, IMHO & YMMV. Only AVS members that are super picky about image quality (and there are a lot of them) can really benefit from the newest models.
I bought my first 1080p PJ last October. Would I like a new one, yes, definitely! Would it really look better than my existing one (in my normal viewing environment), highly unlikely. Until there are major improvements in the technology, I'll be satisfied with what I have for another year or two, at least.
Studio2000 -- As I said before, you look for better black levels & detail in the shadows (in darker scenes). Don't fret about excessive image brightness. All PJs have adjustments to reduce the screen illumination to satisfy your needs (especially in your light controlled HT room). The only thing you have to worry about is if the PJ is bright enough to give you a satisfying picture on your sized screen in your viewing environment. Only you can answer that question.
Almost all PJs are bright enough to light up a 100" to 110" screen. It's only when you want to project from the maximum projection distance onto a very large screen, that the lumen output may not be sufficient. That's why you need to read the reviews on the PJs you are considering. I recommend Art's reviews -
www.projectorreviews.com (he does a very thorough job of covering the details).