I have a suggestion which I feel would improve the tag searching on the 3 sites, and allow you to combine tags without the search box. The UI I have in mind is 'borrowed' from Delicious and is basically a crumb trail that you can click and add tags into. I'm sure they took it from another source however, and isn't their own creation. For a demo try here.
This could sit underneath tab bar (stats,newest,hotest etc.) fairly easily.