I guess is very common there, I'm not sure how common is it in other parts of the world, but I don't quite get what that percent number represent? Or hot to read it?
Less is better I assume from Jon Skeet profile?
Well, the top n users are those n users that have the most reputation. Then consequently the top n% users are those
And yes, lower numbers are better as being one of the top 10 users is clearly better than only being one of the top 1000 users (though obviously any member of the top 10 is also in the top 1000).