The new tagging feature in WordPress 2.3 was kept purposefully simple. We focused on providing infrastructure that cool tagging plugins could use. As noted by Weblog Tools Collection, there are already two tagging plugins that work with 2.3. Advanced Tag Entry and Click Tags are from regular WordPress contributors Jennifer Hodgdon and Andy Staines. Check these out if you want something a little fancier than what is built into 2.3.
Watching to see how plugin authors enhance tagging will be fun. Some of the most popular features added by plugins will likely wind up in 2.4. I like releasing something simple, letting plugin authors innovate and extend, and then pulling the best and most popular stuff into core WP.