One limitation I find in the SCM is that, like Add/Remove Programs, it requires that the service exist and be functional enough that it be able to uninstall itself.
So if I install something, and then blow away the directory it's in, there's no way to remove the service entry from the Services control panel. I have to hack it out by hand with RegEdit.
What happens to me more often is I create a service, install it, and then some time later, decide to change the name. If I forget to remove the service before I rename it, I end up with the service entry under the old name as a zombie that I can't remove.
It'd be nice, in both those places, for the OS to offer the ability for an admin user to say 'hey, the app is gone, take it out of this list'.