In walking through Brian Desmond's excellent post on IIS and UNC permissions, I created a new application pool, gave it the service account's identity, and set the particular site to use it. When I tested the reconfigured site I got a nasty ol'
Service Unavailable
in big Times Roman bold font. And that was all I got. Almost made me want to see another ubiquitous W2K3 404 page.
In retracing my steps I discovered that I did not set the user account's password in the Application Pool setup. It seems that W2K3 pre-fills IIS password fields with ******* (dots, actually) which makes it easy for me to forget to enter the password and think I already did it. In W2K IIS dialog boxes, password fields are by default blank, so you know you need to enter a password.
That as an aside, the point is that a Service Unavailable error in conjunction with Application Pool changes may mean there is a problem with the account. I read on a google post that the C:\windows\system32\logfiles\httperr file might yield info on any application pooling errors, but it did not provide any clues for me in this case. I'll definitely go back and check out some of the new W2K3 logging services.