I've changed the way favtags are calculated such that the background process recalculates the tag query every time it runs. Hopefully it'll be more reliable. It may take an hour or two for everyone to get updated.
I've also improved some of the reports (http://danbooru.donmai.us/report/tag_updates ). I've added wiki and uploads, and you can now specify a date range and how many rows you want (limited to 100). I got rid of the pie charts since, while pretty, they took up a lot of space and didn't convey much information.
As always, let me know of any issues.
Updated