Microsoft’s free PC Advisor (download here) falls into the ‘does no harm and just might help’ category. I would recommend it to friends and family who find their computer is having problems. Hey, it can’t hurt.
I downloaded it (here) and installed it all of my Vista 64 and XP machines. I run a pretty tight ship so I wasn’t expecting much. As you can see from the pictures below, it recommended I take certain actions to speed up my PC, clean things up, update software etc.