Perhaps Ubuntu isn't the best thing for all users – lowendmac.com thinks it should be used with caution.
Read about it here
Does Ubuntu Linux make any sense for Macintosh users?
In my friend's case, I would say no, and I did.
He's an experienced, but not especially tech-savvy, non-power user, and the geek aspect of Linux would be of no interest or service to him. The machines he has are powerful and up-to-date enough to run OS X very comfortably. He has a suite of Mac software, and I can perceive no advantage and many potential pitfalls in his switching to Linux.
On the other hand, for users of older Mac hardware, particularly machines not supported by OS X, Linux is a way to give them a new lease on life with a modern, secure, and robust operating system that requires less power and processor overhead on their less-than-cutting-edge equipment.