Mac's don't need defragging as OS X automatically writes 2Gb or below sized files to one contiguous space on the drive. There are certain cases where's it's needed to free up a large spaces on the drive, but not something everyone has to do.
Far as other Mac maintainence, there really isn't any except to backup one's files regularly. Keeping Software Updated and run a web browser check to make sure the plug-ins are current.
For Safari and Flash, this check is more accurate
Most of those cleaning programs are junk, especially MacKeeper.
If your friend got onto your computer and visited a bunch of adult sites, then I would recommend something like OnyX, doing ALL the cleaning and maintenance aspects and rebooting, perhaps followed by a Disk Utility Erase free space.
CCleaner beta is out for OS X, used on PC's and combines cleaning and scrubbing of the drive if setup correctly.
If your interested in performance, read my post here
Actually Mac OS X is good at of taking care of itself, if there are performance issues (like you say cleanning the machine), there are a couple of things you can check:
- Check your Login Items under System Preferences > Accounts to see what you have automatically launching.Also check /Library/LaunchAgents/ and /Users/yourusername/Library/LaunchAgents/ for items launching at startup
- Launch Activity Monitor and change "My Processes" at the top to "All Processes". Then see what may be consuming your OS X system resources.
- Check the System Memory tab at the bottom of Activity Monitor to see if you have excessive "page outs", a sign that you may benefit from more RAM.
- Check if you are running any poor Mac anti-virus programs as they may take large resouces.
If you don't want to do these manually or the above check still won't help, let this utility to clean your Mac and fix relevant issues easily.