http://gmailblog.blogspot.com/2009/03/new-in-labs-filter-importexport.html

That is totally wonderful. The best feature ever. Now I can share a year's worth of filtering with other accounts. All I need now is a macro filter creator, which would apply a predefined set of steps to a group of messages

My favorite detail from the Gmail blog entry is that Google has something called a "Data Liberation team".