In a posting to the Windows in Higher Education Listserv, I was asked about a new behavior in Exchange 2003: Exchange System Manager prevents you from setting the domain name in a recipient policy to the same as the FQDN of any of your servers.  I was the driver behind that change so I take some responsibility for explaining what we were thinking. 

The main problem we were trying to solve is a situation that a fair number of smaller customers were getting into: they install their sole Exchange 2000 server for their domain "gotdotnet.com", and they decide (for some reason) to set the name of the server to "gotdotnet.com".  I would normally expect people to name their first server "mail.gotdotnet.com" and then set up an MX record for "gotdotnet.com" to point to "mail.gotdotnet.com".  Anyway, this works fine until they need a second Exchange server, which they name "mail2.gotdotnet.com".  When a user on mail2 sends a mail to a user whose mailbox is on "gotdotnet.com", something funny happens in the code that determines whether a message is local or not and it says "hey, I am canonical for mail for gotdotnet.com, so I'll just send it to myself", which conflicts with the part of routing that says "this mail needs to go over to the other server" and it eventually NDRs.  This is documented in this KB article

Once someone gets into this situation, the only solution is to move all of the users to mail2, then uninstall the first server and rename it to mail1.  Not a very good procedure.  The most reliable solution we came up with was to prevent them from going down this path - we thought that if only the people knew that they should name their first server "mail.gotdotnet.com" instead of "gotdotnet.com" they probably would - we figured people who did the latter just didn't know any better.

But now I learn via the Windows in Higher Ed list of another way that people used this.  They treat their Exchange servers like many people do UNIX machines: name it foo.blah.com and tell people to mail user@foo.blah.com.  When we think about people using Exchange servers, we typically think of them running them in a corporate centralized environment where the mail comes in to @blah.com and the servers are named mail1, mail2, etc. I think that it's still feasible to make Exchange 2003 do what you want in this topology, but it just shows that people will do things we never expected.