Definitely NOT worth it! Don't waste time or money on it. You really don't need "cleaner" or "maintenance" apps to keep your Mac running well, and some of these apps can do more harm than good. Most only remove files/folders or unused languages or architectures, which does nothing more than free up some drive space. It will not make your Mac run faster or more efficiently, since having stuff stored on a drive does not impact performance, unless you're running out of drive space.
Mac OS X does a good job of taking care of itself, without the need for 3rd party software.
GGJstudios is, of course, correct. However, the fact that you asked if MacKeeper is a scam means that MacKeeper is a scam. GGJstudios's point is that software like MacKeeper is not necessary for MacOS X. He is absolutely correct. However, some users delude themselves into believing that they or their situation is so special that they need MacKeeper even if no one else does. Well, no matter how special anyone may think he/she is, MacKeeper can't help because it is a scam. A sugar pill will do more good for a gunshot wound victim.
Looks cool at first, fooled me. Turns out that not only is it useless, it was killing my computer. Google it.
And here is a link that might help you decide: