Sadly, I didn't even get to read the comic strips that made Angela Gordon of United Feature Syndicate so unhappy. They were presented on my site through IMG tags linking to externally hosted graphics, and those graphics were gone before I got the letter.
The way intellectual property law is going in the U.S., I wouldn't be surprised if these cease-and-desist letters began to be accompanied by a demand to pay for the lawyer's time.
What's an impressum?
Impressum is your personal contact data and address (street address, not only postal address - for example a PO box isn't sufficient!). So if you write stuff people don't like, they can readily send their hitmen towards you ;-)
Be very happy you don't live in .de: around here that letter would have included a bill over some hundred EUR just for the "work" of the lawyer that would have sent the letter and you would have to pay that bill or either go to court on your own money (no insurance pays trademark or property violation cases).
There have been some recent law changes in .de that would help you a bit - in that you aren't responsible for stuff written by other people on your pages, you just have to remove it immediately - but companies often ignore that fact and try to pull that stunt on you nontheless. It's quite unnerving around here sometimes :-/
(you would get problems because not having an impressum on your pages, though - and somebody would send you a bill on that, too)
Currently these "Abmahnungen" are very popular with lawyers in .de - seems like we just have too much of those (lawyers) and they don't find serious work and so try to squeeze some money out of the internet by sueing private persons ...