I took AP US History 6 years ago in HS. I got a 5 on the test, and got 6 credits of history (US History before the Civil War and US History after the Civil War). It was the best dollar for dollar investment I made in high school. I don't know much about the AP European History test. It also depends on what college you are applying to. That is something very important to keep in mind if you need to break a tie between two schools.
UofI- Yeah, I'm going to have to sorta disagree with you on that one... Yeah... Seriously though, I think that AP classes are really worth a person's time if they can't test out of requirements. I am an engineer, and I didn't really want to take my liberal arts and sciences electives. I was actually able to test out of 9 out of 12 credits. So, AP classes in areas outside your planned field of study can be very useful. I also got out of 3 credits of english, and thanks to two summer classes I took, I got out of 6 more credits. Effectively I got out of 18 hours (a very full semester) of classes, which was very much worth my time.
Ryan