<p>So the ADO.NET Entity Framework has gotten a little bit of bad press (in the form of blog entries and a petition) but I don't want to rush to judgement. I'm limited in time for experimentation but I was wondering has anyone worked with it yet with more empirical feedback? </p>

<p>Finally, what are thoughts on using NHibernate which has been around for a long time and <em>may</em> be more mature than the ADO.NET Entity Framework.</p>

Microsoft have all but admitted that the ADO.Net Entity Framework isn't an ORM (I can't find a reference currently). So if you think of the Entity Framework as a query engine then apparently it is really good at what it does. For a complete ORM solution you might want to look elsewhere however.
The following blog post seems to bear out this difference:
http://blogs.msdn.com/dsimmons/archive/2008/05/17/why-use-the-entity-framework.aspx