Is the iOS5 GM identical to the final version? Are there any differences between the iOS 5 GM seed released to developers and the final version released to the public? If I have the GM installed, do I need to do anything?
No changes in file bytesize at least.  The first GM seed for 10.7.2 was initially marginally different to the final version in some way and was updated, but the iOS 5 release is identical.  No need to change anything.  If you were not already on the GM/release version, it would have complained by today and deactivated your phone...