After updating to Mac OS X 10.5.4 (released yesterday), you will want to go to System Preferences > Sharing.
Why? Well, all of my Macs added a (2) to the end of their computer names… spontaneously after updating.
Now, the “(2)” usually implies that the network detected a second system with the same name. However, I think there’s another reason, and its name is Mobile Me.
You may recall from other web sites that Mobile Me requires 10.5.4. I suspect that the SyncServices patches renamed the Mac mistakenly. So, this is still a bug, but I think that’s what is causing it. Of course, some Apple engineer will probably balk at that speculative answer… but they’re free to comment (sarcasm implied) as to what the root cause of the problem is.