iOS 4.3.1 Change Log:
* Baseband updates for the 3GS and original iPad.
* 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 recognizing the gyroscope on the iPad 2.
* Possible fix for iPad 2 jailbreak vulnerability.
We are just guessing the last one, but since the iPad 2 has already been jailbroken, Apple will put in some more security to prevent that. The inside sources says that Apple will release this update within the next few weeks.