Again as in most rollups, product improvements as well as bug fixes were addressed. KB 968012 addresses *60* bugs that were fixed along with a really important update for Server 2008, where disabling kernel mode authentication on cas servers isn't a manual process anymore. Expect this rollup to trundle down via windows Update on or after May 26, depending in your time zone.
As with most rollups, you want to grab them while they're hot since most of them address bugs and or critical issues.. exchange 2001 SP 1 still has a number of issues so I recommend you look the list of issues detailed in KB 968012 and see how they apply to your configuration. Happy patching!