To understand the reasons why many people who will argue strongly for fair use, etc., still find this wrong, you have to look two steps ahead.
Let's say 37 signals has done the extensive work to create a page design that really converts. And we live in the world where anyone else who wants to lift their carefully-researched design can do so in 10 minutes, and reap the same benefits.
Unfortunately, that would put 37 signals at a serious disadvantage -- assuming that customers don't know who first created something really good, the actual creator always loses. All of the copycats get the same benefit with a cost of 10 minutes vs. 10 days.
So the only way 37 signals can benefit from their work is to find a way to make it more work to copy than to recreate.
To do that, they'd need, what -- some kind of heavily-obfuscated Flash? I'm sure if the need were there, we'd find a way to really lock down web UIs.
> In this case, 37Signals was given free rein to track Curebit's customers. Sounds like a good deal to me.
Unrelated to my points above, but never mind tracking... a hotlinked image is the perfect invitation to tweak your own layout, then change the original image files. Sadly, it looks like 37 signals missed their opportunity to paper over Curebit's page with animated penises.