So much to learn!
I only followed halfway of the rabbit hole about the idea of "composable data (entity) services" and found that much has been written and debated about the topic. It seams, for instance, that part of the SOA intelligentsia has been discussing if the concept of entity services could be some kind of anti-pattern.
On the other side, I think Astoria's value proposition is very solid, at least for the scenarios currently targeted (which I think are more oriented to mashups that do all data aggregation on the client side). Also, Pablo Castro addressed some of the concerns that could apply to Astoria shortly after MIX07 on his own blog.
The Entity Framework is also such a distinct beast, that could shift the balance on what is a good practice (i.e., by making entity services very easy and inexpensive to own).
I would really like to get the whole picture, but this will have to wait for now...