Recently we discovered a problem related to user profiles when installing the October 2010 CU for SharePoint Server 2010.
The October Cumulative Update makes some changes and updates to the user profile database. Unfortunately there are certain situations where this update does not complete as expected and leaves the update in an inconsistent state. This causes issues with several SharePoint features that use the User ProfileApplication such as MySites, People and Expertise Search & Ratings.
All the details about the issue including a workaround to overcome the problem can be found in the following blog post published by the SharePoint product group:
The downloads for the affected packages (SharePoint Server Package 2394320 and Project Server Package 2394322) have been removed from our download servers. If you have already downloaded them you SHOULD NOT install them. They will be republished.
Customers who installed October 2010 CU should review the information on the above listed blog post!