I think I've come to the decision to treat 3.5 and 4.0 as two separate games that happen to share a similar (though not identical) implied setting. I still have a lot of 3.x edition stuff I want to run, and I want to do it without having to do massive amounts of converting, so I'll probably run both. Rise of the Runelords and Age of Wyrms are both too good not to play, so there are two campaigns I'll be running for sure. Then I probably have at least 2 or 3 campaigns worth of material from Necormancer that remain unplayed. Finally, there's a whole boatload of Dungeon magazine adventures.
In short, I probably have a few years worth of life in 3.5. Fortunately my players have always been interested in playing different game systems. Right now we're in the first third of a True20 Darwin's World campaign. Did I mention that I have no intention of ditching the True20 either?