The release notes for this update include: disabling out-of-date iTunes plug-ins, fixes to drag/drop, fixes upgrading encrypted iOS devices to 4.0, and increased stability. If you use iTunes at all, it is in your best interest to grab this update for Mac OS X 10.4.11+ and Windows XP SP 2+.
I think this shows that Apple is moving in the right direction with their release notes. We’re pretty used to reading barebones summaries, and this is clearly enough information to gauge whether or not you need to upgrade right away. Let’s take this opportunity to applaud Apple for listening to the community.
After you install 9.2.1, please leave a message on this post to let us know any of the issues you came across. We’d like to know how your experience went.