If you have used the normal Add/Remove programs function in windows (the Programs and features in case of Vista) you may not be uninstalling a program correctly. Most of the programs that get uninstalled end up leaving broken links and unused files. Most programs often leave big unused registry entries. This can sometimes considerably slow down your system.
To protect your system from this, use Absolute Uninstaller. This removes all unused files and even cleans up broken registry entries. All this will be done in seconds. This program starts faster than the Add/remove programs works faster and cleans better. This also provides a user-friendly list of programs with identifiable icons and it also has a useful search function to search for additional programs that are not listed. The search functionality lets you search for applications that may not get listed. The overall functionality of this application is commendable as it is a light weight application that can do a very good job of keeping your system clean.