very good!
It's high time that we need samples like this (I remember an very good series of blog posts by Brad Abrams)
I'm actually working on an enterprise app that use nHibernate as DAL and WCF RiaServices on the wire; I've got to say that it's more tricky that is seems at a first glance, primarily: limitations on the generated DomainContext (just today I'm excited about the release of sp1) and performance issues when loading complex object graph... (eager/lazy load)

But despite this, nHibernate and WCF RIA are a great pair!