After updating to iOS 5.0.1 via iTunes and rebooting, I found all the App Store apps installed on my iPhone were suddenly waiting to download. That's right. All of them. Just "Waiting". Unable to launch.
I tried force-quitting the App Store app. I tried rebooting. I tried resetting. I logged into and out of the App Store app. I checked if there were any iTunes Store downloads, like podcasts, that might have gotten "stuck" (there weren't). I checked if any large apps like Navigon were slowly -- very slowly -- downloading (they didn't appear to be.) I tried re-syncing with iTunes on my desktop (the apps came back, still waiting).
I could still download new apps and those worked fine. They actually downloaded quickly, installed completely, and launched properly.
With 5 pages of apps, it's going to be a pain to delete them all and re-download them all one by one, but it's about the only option I have left right now.
Note: Like I said, the first two didn't work for me but they were offered as potential fixes on Apple's discussion forums, so if you have the same or a similar problem, give them a try before you escalate to the last one.
If anyone else has figured out a better solution, let me know in comments!