The update in question was released on December 14th, there are three main issues associated with this update, these include connection problems with accounts which use SPA, slower performance when switching between folders and also AutoArchive no longer working.
Microsoft recommend that you uninstall this update, to do this on XP open up control panel, select Add or Remove Programs, tick the “Show Updates” box and then select KB2412171 and click remove.
Vista and Windows 7 users should open up the control panel and then click Programs, under Programs and Features click “View installed updates” and then click on the KB2412171 update and click uninstall.
If you check out this link you can find out more about this update and how to remove it, ironically the official description of this update says that it features stability and performance improvements you can see full details regarding what this update should have done here.
Did this update cause you problems?