If you need to link in a person’s current avatar in your web app, @raffi added a neat little trick to pull in a couple different sizes. Very handy!
http://api.twitter.com/1/users/profile_image/damon?size=mini
http://api.twitter.com/1/users/profile_image/damon?size=normal
http://api.twitter.com/1/users/profile_image/damon?size=bigger
It does a 302 to the current avatar image file on S3.