Should a "waiting" icon appear as an App on your iPad, and refuse to be deleted even after doing the icon jiggling trick (no "x" will appear) - it is likely waiting for a wi-fi connection in order to download a file larger than the 3G limit (about 20 MB.) Either connect to a wi-fi network to complete the download, or:

• sign out of the App Store
• do a hard shutdown (i.e. hold down Home and on/off buttons simultaneously, and do not use the slide to switch off: it will eventually power down b...