That was actually a hard to implement feature, since this is not something that NHibernate just give out. Nevertheless, by trawling through the codebase long enough, I was able to figure out how to do this.
As an aside, one of the requested features for NH Prof was to be able to get DB level stats. I am not going to do this for v1.0, but I now have a pretty firm idea about how to implement this. We will have to see how many people request this information.