AppEng 1.1.2:
googleappengine.blogspot.com
batch writes: include entities in different entity groups in one db.put() or db.delete()
googleappengine.blogspot.com
I was originally excited about it, but the performance and limits have kept me from feeling comfortable hosting something substantial there. This feels like maybe an odd bias that stems from it not being as awesome as I wanted it to be, so it'd be great to hear some successful anecdotes from others here.
I'll report on a more substantial app once it gets some testing.
A good list of apps on App Engine: http://appgallery.appspot.com/