Rackspace recently announced that they'd like to discontinue Slicehost at some point, migrate everyone to the EC2-like Rackspace Cloud, and make people worry per GB about the bandwidth they're consuming. So I'm preparing a move to Linode for more of everything*, and in the planning, I've come across a new argument in favor of whimsical names for servers.
If I give each server a whimsical name, like alice.example.com and bob.example.com, I can always refer to the old and new IP addresses as "alice" and "bob", while the change of IP of "www" propagates through the DNS. Between the time where the new address is set and the old one is expired (and note that there's no way to force an ISP's resolver to honor the TTL if they choose to assume "no TTLs will be shorter than an hour") the name being transitioned points to a more-or-less random server.
Basically, the whimsical name is like a server ID, and the service-based names are just conveniences. Though a program is three lines long, someday it must be maintained; though a server hosts one service, someday it will have to be replaced. When an organization gets big enough that it can't generate whimsy as fast as it needs servers, then it should go with something more regular for the server name, but each server should still have a unique, non-service-based name.
* Except bandwidth, but the 11% difference is smaller than my current monthly consumption, so it turns out not to matter much. Even if it did matter, that much transfer on The Cloud (insert angelic chord here) would be expensive, so Linode still wins.