A while back I gave up waiting for Blogger to add the ability to tag posts and started using a Greasemonkey script that let me assign tags to posts (I've got a list of basic tags I use here). The new Blogger has a built-in capability to label posts, and thus while the Greasemonkey hack has worked well, I'm going to stop using it1. It should be relatively trivial to go back and move the old tags into the new Blogger system, but doing so will take time (which I'm sadly short of these days).
I'll likely have both tagging systems functioning for a while; I apologize for any confusion this causes.
1 Sorry, del.icio.us.