When I was looking for inspiration I actually looked at doing a 'top genre' thing but I didn't do it mainly because it had already being done, and at the time it was plastered over quite a lot of people's profiles. Also, perhaps, doing this wasn't complex enough for my documentation (loop through each artist, keep a cumulative total of tags).
Oh and by the way I noticed this post in your blog, a venn diagram like that of your last.fm charts would be awesome.