I don't think it has liquid database scaling the way App Engine does. If you have to even spend a second thinking about sharding, partitioning, replication lag, etc. then you're not getting the same functionality.
My experience with App Engine is that you have to think pretty hard about sharding and partitioning - the hierarchy part of the App Engine data store controls which bits of your data live in the same place, and hence what can be modified in a single transaction.
