I can name several: Christmas, Boxing Day, Winter Break for university students, and New Years. Hence, "it's the holidays."
The trouble occurs when users reinstall XP's system files using the repair capability found on genuine XP CD-ROMs. (The feature is not present on "Restore CDs.") The repair option, which is typically employed when XP for some reason becomes unbootable, rolls many aspects of XP back to a pristine state. It wipes out many updates and patches and sets Internet Explorer back to the version that originally shipped with the operating system.
This issue highlights why it is vitally important that Microsoft doesn't release undocumented updates on the sly. Even the best tested update can have unpleasant side-effects, but if patches are documented properly and released in such a way that users (especially IT professionals) know they exist, it offers a necessary starting point for troubleshooting.
It is not best to swap horses while crossing the river. -- Abraham Lincoln