Is it technically illegal? Yes. Is it taking money out of anyone's pocket? No, not in any way that I can think of.
...a lot like our site, wouldn't you say?
Well, this site is more gray area since we don't attempt to make any money from what we do. If anything, it would be more of a civil matter than criminal. Even then, it would be REALLY difficult for the plaintiff, whoever they may be, to prove that this site has caused a monetary loss for them. Someone such as an artist who's work we've employed in our covers, or a company that doesn't like our use of their logo, etc.
Covers like mine are even more legally ambiguous. I use logos that I find on the web, art that I create or find on the web, and almost nothing of the original packaging from scans. The barcodes are the ONLY thing that I'm using at this point, and even then, I still have to make 'em from scratch when no scan is available using what UPC data I can find for the title and the appropriate fonts to recreate the barcodes.
I don't know if this site has ever been threatened with any sort of legal action, but I have to imagine that any half competent civil attorney wouldn't do much else besides sending a threatening email/letter as a scare tactic. Anything beyond that would be a waste of time, and he/.she would know that.