TwitterScore s your public profile to give you a score out of a possible 10. It then shows you a graph, your rating and also people in close proximity that you may want to follow. I noticed all of them had high scores via this site.
The site is ad driven and they are all over the place, so watch where you just click. You also have some menu items to see Top Users and Top Locations. Depressingly the top 50 were almost entirely celebrities, with a bunch not even doing their own tweets. Ugh.
The US was the top ranked location by a far reach with the UK in second. It was a quick interesting browse but I wished it told you how to increase your score, or how it even decided how to build the score. A lot of unanswered questions and you should know how to find all of the top 50 already.
The benefit was the local map where you could find a handful of people you may not know about that were rated well.