In addition to uninstallers, and as much as I hate to admit it, I favor a registry of sorts.
Not for settings as in windows, but more specifically so an uninstaller can locate the files to uninstall, and so that Softare Update can also locate installed packages.
This annoys me greatly, because I like to organize /Applications into a hierarchy by category. I know, I know, spotlight, saved searches, etc. But some habits are hard or impossible to break.
It would also be a treat if 3rd party developers could provide an update URL in said registry, and Software Update would iterate through said URL's, such that one single Software Update mechanism is used for all software.
Forget the Leopard Bells and Whistles, Just Give Me an Uninstaller