When you run the program for the first time it will advise you of the state of your registry, normally suggesting that you run an analysis to attempt to clear out any errors. In this way, a couple clicks will let you clean up your system registry and leave it like new.
The program options, which are rather more advanced, will let you list exceptions so that during the scan process particular entries to your registry are not touched, something that might prove quite useful to certain users.
Registry Life is an excellent choice among the most well-known registry cleanup programs. Easy to use and very light to run.