In general, deleting stuff outright will often not work as you'd expect.... true, our system could work a little better in this regard... but I'd generally avoid deleting stuff. If you want mtaylor back, write support and they can probably delete it for real so that you can re-add it. Be kind to them though - with the recent promotion, support is really busy today.
michael won't work since (for one thing) michael is one of the owners of the company, although he doesn't seem to have a user on that particular group of machines :>
In regard to the previous comment, usernames aren't unique per machine; they're unique per "cluster", which is just an internal logical grouping of machines. Each cluster has its own namespace.