I had to completely remove and reinstall the Facebook app from scratch on both my Verizon iPhone 4 (4.2.7) and my wifi-only iPad 1 (iOS 5 GM) to get it to work.

I had to completely remove and reinstall the Facebook app from scratch on both my Verizon iPhone 4 (4.2.7) and my wifi-only iPad 1 (iOS 5 GM) to get it to work. The iPhone just sat and "pinwheeled" for 4-5 minutes, and the iPad would dump back to Springboard on launch.