MacKeeper is highly invasive malware* that can de-stablize your operating system. It is also unethically marketed and a rip-off. Positive reviews of it are known to have been paid for by the developers, Zeobit.**
Further opinion on it and how to uninstall MacKeeper malware:
http://applehelpwriter.com/2011/09/21/how-to-uninstall-mackeeper-malware/
Do NOT download or use the ‘MacKeeper uninstaller’ from the Zeobit site, as this will cause even more damage to your operating system.
This is also worth reading:
http://www.reedcorner.net/news.php/?p=245
Equally phoney is iAntivirus:
http://www.reedcorner.net/news.php/?p=341
* The expression ‘malware’ is a general term used by computer professionals to mean a variety of forms of hostile, intrusive, or annoying software.
** Possibly including positive comments by certain posters in this thread.