The best safety measures are all preventative.
Personally, I think that basing a car's "safety" solely on it's crash worthiness does not provide a clear image of what exactly a safe car is.
If they were to figure in such other important factors, such as braking distance, how loud the horn is, and manueverability, size of blind spots etc. - we'd get a much better picture of what a safe vehicle is (hint: SUVs aint safe)
So check the road test data as well - and don't be afraid to test the horn either!
Also, I'd discourage buying a car (especially a compact) painted a dark color, especially black or dark blue. Bright colors are more noticable, not only by the police - but also by soccer moms chatting on their cell phones while trying to merge their Excursions into your lane (and into the side of your car!). If they still don't see you - lay on your horn, and give them the finger.