I totally agree that there's a lot more to do! I have such a long wish list for this project. The only problem with charts is that the Terms of Service for last.fm states that chart data is to be cached for seven days (so it can't be updated daily). see http://www.last.fm/api and http://www.last.fm/api/tos
but if you have concrete ideas of which api methods to use, and how to display the data, feel free to post! (and remember that it's open source, so you can start hacking on it yourself! and I'll incorporate your code into the project if it's well written and follows the general code standard. see https://github.com/hakko/musiccabinet)