Many, many props to NevOn, who had pretty much the same issues as I've had:
NevOn Experimental: Domain mapping still doesn't work properly
NevOn Experimental: Domain mapping now active
Update with another link on this topic: Blogging Business: Domain Mapping With Typepad.
My own error had been a "www" CName entry that was not pointing to antsaint.typepad.com. Hopefully all will now be well... but we shall see in, oh, about 24 hours or so (give enough time for DNS stuff to fully update/resolve).
