I almost feel bad for these guys but I understand why DHH was so pissed. Getting inspiration or even straight up stealing the HTLM and CSS is one thing, but referencing assets on 37signals servers is beyond the pale as 37signals is paying money to serve those assets.
This happened to a company I worked for, a company not only ganked our website but used pictures of our offices and staff we had on our about us page!
I've had this happen and they were actually using a sizable amount of bandwidth.
The great thing about it, though, is that you can move your originals and change the hot linked images to something else. Like a message to their customers, gross pictures, etc. it can be a hilarious opportunity to mess with somebody who is stealing your stuff!
This happened to a company I worked for, a company not only ganked our website but used pictures of our offices and staff we had on our about us page!