Sometimes when you've got multiple downloads going on, it will create a "lag" -- also it could well be updating them, you only see "Waiting" on the ones that have not caught up in the download queue yet. I would recommend giving it some time, at least 30 minutes if you have a bunch of apps to update at once, and a slow connection.
Another thing could be a connection problem grabbing one of the apps off of Apple's servers which is stalling the process altogether.