Mark has released an Atom 0.2 Snapshot. It includes some changes from the 0.1 snapshot, and also omits some things that are still in flux on the wiki.
I was able to produce a valid Pie/Echo/Atom feed in just a few minutes using MovableType. All I did was grab Mark’s template, two plugins: UTCDate and LastModified, and rebuilt my indexes.
It should also be trivial for TypePad to deploy Atom 0.2 feeds system wide. I would assume a blosxom (or similar) template wouldn’t be hard to put together either.
It just gets better from here.