1. With a lot of people picking up new iPads and downloading directly to the devices, it's causing a massive hit on Apple's iTunes servers.
2. You can pause/resume any/all pending downloads by just tapping on the icon. One tap will pause the download, one will resume. Sometimes you can just pause all of the apps except one and then it will start downloading again. This seems to be because all the apps are trying to queue for download at once, overwhelming the connection to the iTunes store that authorizes the downloads.
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.