Someday when another project requires extensive logging like the one I'm rolling off soon, I'll have to give NLog a look. Compare it to Enterprise Library logging application block.

At a super quick glance, they're similar. NLog supports async logging out of the box (sounds like it's just a background thread, so messages could be lost if process shutsdown quickly?), and apparently very efficient filtering (throwing away messages that don't meet specific criteria, not worthy of being "logged" to their destination).

NLog - Introduction