But Gmail already does allow sharing of email filters. It's something they added recently, I think - it's still in the Google Labs tab. It's called "Filter Import/Export."

(Edit: that's the cool thing about Gmail, really - if you can think of a feature, they probably already thought of it, too.)

Edit #2: looks like it exports filters in XML, which is nice. Here's a pretty good overview of the feature:

http://googlesystem.blogspot.com/2009/03/export-gmail-filter...