Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Cocktail does nothing that you can't do with a terminal command. If you really want to a utility like this, then you should use OnyX. It is not better than Cocktail, but it is free.
 
I still have it installed, since I bought it a few years ago. Can't say I use it these days though. It does what it says well enough, but you can do it all yourself with a bit of Googling and the Terminal app.
 
Yes, but it's nice to do stuff like that at the click of a button (plus if you're scatterbrained like me, you're less likely to forget to run something if it's all right there in front of you). I still use it every now and again, it's a good little app.
 
I got a Cocktail serial in the MacUpdate promo last year. It works when I use it but I'm always wary about "system utilities" and the "Repair Disk Permissions" panacea.

Always have a backup.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.