Here are the changes from iOS 4.3:
● Baseband updates for the 3GS and iPad (original)
● Fixed memory hang that results in memory corruption when reading large files from USIM filesystem
● Fixed problem with NTLM authentication in apps and on websites
● Fixed issue with the Springboard and 3rd party apps not recgonizing the gyroscope on the iPad 2
● Fixed iPad 2 jailbreak vulneratbility
It's unclear which iPad 2 jailbreak vulnerability is being fixed by Apple since none have been released yet. It was thought that Apple would be fixing the Safari based exploit used by Charlie Miller to win Pwn2Own with the 4.3.1 update.