iOS 4.3 has only been available for about two weeks, having been originally released on March 9th just prior to the introduction of the iPad 2. While relatively few issues have been reported with the new OS version, BGR suggests that iOS 4.3.1 is expected to arrive in the next one to two weeks.
While this is expected to be a fairly small update, BGR says that it will provide baseband updates for the iPhone 3GS and iPad, fix a memory hang that results in memory corruption when reading large files from the USIM filesystem and resolve a problem