I recently switched about 40K images over to S3 almost flawlessly with paperclip (great job). If I could go back and change my implementation I would have used the style for a filename, but in my scenario I have users uploading images like "tape measure.jpg". The thumbnail saves fine, but when you use the url helper it doesn't know how to correctly substitute the space in the url with "%20". My work around for now is to do the following...
image.url(:thumb).gsub(' ', '%20')
This seems to work fine, but I thought I should pass this on. I'm using the most recent version of paperclip as a plugin, not a gem.