I've been having a problem with installing and updating apps after upgrading to iOS 6 on my iPad (3rd gen). When I click the
Update button the button, it turns inactive with "Installing" word on it, while the app's icon on the SpringBoard says "Waiting".
I tried even buying a new app, but it is exactly the same. Deleting the app and trying again doesn't help. What's interesting the problem doesn't seem to affect my iPhone 4S.
I noticed several people at Apple Support Communities are affected by this, too.