With iOS 5 it's not uncommon to sometimes see the label under many apps, including Facebook, sometimes change to read "Cleaning..." This is a feature of iOS 5 that Apple hasn't really explained, so it's caused a lot of you to write in an ask about it. Here's the deal...
Basically, that's iOS 5 deleting cache and temporary files so that when iCloud or iTunes does a backup of your iPhone, iPod touch, or iPad, that backup is smaller and faster.