I've only just read through the blog post describing it, so I can't say that I've used it, but it is of some interest, as it is designed to provide:
- Change tracking (snapshot-based and proxy-based when possible)
- Transparent lazy loading
- Immutable Value Objects
- Queries (LINQ and Entity SQL)
- Shadow state (maintaining certain persistence-related fields outside of entity class)
I don't think in the long run it will be satisfactory enough by itself to make people switch from NHibernate (in a way, it's implementing a mapping on top of the already over-abundant mappings required in EF), BUT if it is used/eventually becomes how EF implements native POCO support in v2 (its described as a vehicle for providing feedback), then MAYBE it becomes a bridge to use in the interim (did I hedge that enough?).