Powerful Gmail Feature, Adding Suffix To Your UserID

Gmail has an incredibly powerful, yet somewhat unknown feature, that allows you to append a suffix to your userid. This combined with a filter makes for incredibly powerful spam control!

yourid+suffix@gmail.com

The beauty is that you can use as many suffixes as you like, ideally one for each of your services:

yourid+twitter@gmail.com
yourid+flickr@gmail.com

This way (god forbid) if one of these services sell your email address to a 3rd party, it would be very easy to track down the culprit.