Hi,
For those who know the inner workings of nhibernate, do you think a large scale web application like say facebook/myspace would use nhibernate?
Or is nhibernate well suited for more low traffic sites like company sites etc? i.e. not enterprise ready because of its chatty nature?
NHibernate is not chatty at all. About scalability, there was already a question on NH's groups, which was more about the complexity of the database then traffic, but might still be interesting for you.
Even if there are always complaint's about unnecessary queries on every ORM, because of the generic nature of an ORM, it doesn't mean that it is chatty. On the other hand it optimizes situations where it would be too complex to optimize in hand-written DAL's. Eg. query batches or lazy loading.
NHibernate is quite light-weight compared to other ORM's and compared to it's powerful features.
NHibernate (as any other ORM) could be considered to be overkill if there is no object oriented business model but you need to optimize for highest performance. I don't think that Google could make use of NHibernate for its search engine, for instance.
Edit:
The performance and power of NHibernate is not fully for free. It requires that the developers understand at least the basics about relational databases. Other ORM's try to hide the whole relational problematics, which leads to much more unoptimized behaviour.