I just got back from a 2 week vacation in Washington DC.
While I was there I visited the U.S. Patent and Trademark Office Museum in Alexandria Virginia. If you are in Alexandria and have a few minutes to spare, by all means go. However, I don’t recommend making a special trip. It has exactly three exhibits. Two of which are video presentations. The third is a large board listing some patents and how they are related to other patents. There is some interesting information, but nothing to knock your socks off.
After two weeks in DC with my wife and kids, I have to say I did see a lot of other really cool stuff. If you get a chance to be in DC make sure you go to the Library of Congress, and take a tour. It is pretty cool.