Make sure to also check out our very cool thread tagging and tag search system for vb3.6
here!
It allows your members to tag threads and provides a fully integrated search engine - similar in appearance to this mod - which also shows a tag cloud and related tags and provides advanced seach options.
Tag links can use mod_rewrite or standard links and there's lots of options to play with in the control panel. Your tag cloud can easily be put on any page you want - even on other sites!
Tags are stored locally in your db as well as indexed by boardtracker and again all the heavy work of searching is handled by our servers!