I would have thought that it would be possible to have some way that people who like to keep thing neat and tidy to push a button to get all the tags sorted out automatically. All the threads without tags would be in a Miscellaneous list (but divided music and BS).

This is standard feature for almost every forum software out there. There are catagories, sometimes called forums, sometiems call prefixes in Mudcat. Your cookie has a time stamp of the last time you visited. You can see which categories have new posts, jump to new posts in specific threads -- a nice feature for those long threads -- or you can choose to view all new posts since the last time you visited (sorted by thread) jumbled all together. Perfect for those who want everything jumbled together, sorted for those who don't. Programmatically, the different views are simply slightly modified statements with different grouping and sorting clauses.