I've just spent a few hours re-tagging a few hundred questions on serverfault.
Mostly this was to remove 20XX tags, and as they can be ambiguous (eg SQL 2008 vs Windows 2008, etc.) there's no easy way to automatically re-tag, but it makes sense that people create them.
It would be great if they could be blocked with a specific message, something like "Years are not useful tags, you probably are referring to a software version, if so use the full name as the tag, for example: windows-server-2008, exchange-2007"
This is somewhat a dupe of: What can be done about ambiguous tagging?