My iPad 1 runs iOS 5.0.1 but I believe I have had this problem with previous versions. I'll go into the App Store and find a lot of pending updates. I'll tell it to update all and then leave it on to do its updating.
Later (hours or days even) I come back and all or most of the apps that were updated have the faded icon and an empty update bar with a caption of "Waiting . . ." None of them are updating. I tap them and it doesn't launch and doesn't change the status. I've tried rebooting the iPad but that doesn't seem to help.
Eventually it will return to normal, but I have found no rhyme or reason. I am on 20 Mbit DSL so it shouldn't be that it takes days to download a few updates. I don't think that is what is happening anyway because I don't see any progress on any of them.