silkroad - I recently moved just about all my js files and images to amazon s3 w/ cloudfront - results are good so far. This took an additional 4-5gb a day off of the database server (where they were previously being served)
Basically all I did is search templates for "clientscript" and added the CNAME I created for cloudfront in front of /clientscript
I would like to figure out how to move avatars and other 'dynamic' images over to s3. I read through this thread wich looks like didn't result in much:
http://www.vbulletin.com/forum/showthread.php?t=302300