We'd also suggest to make sure that the search function can be easily added to in the future to take tags into account. At least, from what we understood, you're not planning to include tag search yet. It would therefore stand to reason that it would benefit all if the search system did not need to be completely rewritten later when you do include tag search in it.
Also, one thing we do wonder a bit on... Do you think that it is possible to auto-apply certain tags to older topics? Some sort of script to browse topic titles and add a few general tags as necessary? Or would such a feature be more effort than it is worth? A good year of backlogged topics without more than the Casual/advanced/free tags would restrict somewhat on topic results.
Also, one thing we do wonder a bit on... Do you think that it is possible to auto-apply certain tags to older topics? Some sort of script to browse topic titles and add a few general tags as necessary? Or would such a feature be more effort than it is worth? A good year of backlogged topics without more than the Casual/advanced/free tags would restrict somewhat on topic results.