Mac OS X only requires that you drag the application to the trash and any files left over will not have any impact on installation of new packages. This works most of the time, however in some cases we have found that manually removing all related files will actually result in a better chances for installation success.
Apple does not endorse the use of uninstallers, however if you are looking for a universal uninstall utility for Mac OS X, there is this utility called UninstallPKG from CoreCode that has a free trial and while is a paid application, works pretty well.
You can find more information on it here:
http://www.corecode.at/uninstallpkg/