I agree you can't wait forever. I'm making a decision in 30 days time.
I have pretty much resigned myself to the fact that whatever/whenever the 5D successor is announced, it's just not economically justifiable for me, given my skill level and my intended uses. I love shooting landscapes and am working on portraits, so full frame would definately be best for me, but it's not as if I can't take good shots of either subject using a 40D. For the price of a 40D, I can add a great lens, like the 18-55 f/2.8 IS EF-S and still be under what it would currently run me for a 5D. That being said, I could manage a 5D and another lens, if I really felt the need/want for it.
In an ideal world, the 40D would be sold at Costco as soon as it launched, and I could get it and have a month to practice, a vacation to try it out on, and then I could decide whether or not to keep it just in time for the fall rebate period, in case Canon included the 5D to clean inventory. But that pretty much ain't going to happen ... so instead, I basically have to troll the in-depth previews, see what the early word is on a 40D and then make the leap one way or another.
It's funny ... I've been waiting since February to buy new gear, and I'm still not 100% sure where I'm going - Full Frame vs 1.6 Crop (or if full frame, 24-70 f/2.8 versus 24-105 f/4 IS).
By my count, I have now put more time and energy into deciding on what new camera gear to get than I have buying either of my first 2 houses, picking a law school to go to or choosing names for my children. Weird.