I have tried it a few times but personally found it a little to robust for my liking. IMHO care needs to be taken as what you delete as I think it messed my registry up on one occasion. I use WinRescue registry backup program so it wasn't an issue, I also use Acronis backup also.
But if you have no registry backups make one before using this program (or any registry cleaner for that matter). I know some users on PCA have used RegSeeker for years with no problems so I could be a little paranoid.