One word of warning first, this feature is currently for entities only, NH Prof cannot (currently) inspect cached queries. That said, I am working on it, but this is something that is going to require some changes to NHibernate, so it is a feature that will be available on NHibernate 2.1 only.

That said, you can see the profiling result of this piece of code:

public class LoadEntityByIdFromSecondLevelCache : IScenario
{
	public void Execute(ISessionFactory factory)
	{
		int id;
		using (ISession s = factory.OpenSession())
		using(ITransaction tx = s.BeginTransaction())
		{
			id = s.CreateCriteria(typeof(Blog))
				.SetMaxResults(1)
				.UniqueResult<Blog>().Id;

			tx.Commit();
		}

		using (ISession s = factory.OpenSession())
		{
			var blog = s.Load<Blog>(id);
			Console.WriteLine(blog.Title);
		}
	}
}

And, the actual profiler output:

We can clearly see that we loaded this entity from the second level cache, and that we didn't hit the database.

This is awesome, even if I say so myself.

Update: Here is the test for this feature:

[TestFixture]
public class CanDetect2ndLevelCaching : IntegrationTestBase
{
	[Test]
	public void Will_detect_entity_load()
	{
		ExecuteScenarioInDifferentAppDomain<LoadEntityByIdFromSecondLevelCache>();

		var first = observer.Model.Sessions[2]
			.Statements.OfType<StatementModel>().First();

		Assert.AreEqual("2nd level cache load Blog (1 /* id */)", first.Text);
	}
}

You might notice that this looks like it is traversing the UI. You are almost correct, it is traversing the View Model, which is an extremely rich model that allow us to do things like on the fly updates to all parts of the UI, Linq reporting and other nice stuff.

Among the most important benefits that it has is the fact that this is an end to end test of the system. From another app domain executing NHibernate code to the view model being updated by the profiler.