Is Ubuntu Linux a Sensible Alternative for Mac Users?

A friend of mine phoned to ask if I thought he should install Ubuntu Linux on his Macs - a 1.33 GHz G4 iBook currently running OS X 10.4 "Tiger" and a 1.25 GHz Power Mac G4 tower with OS X 10.3 "Panther" installed.

My friend had read a feature in the local newspaper extolling the virtues of Ubuntu Linux and thought it sounded interesting.

Ubuntu is a other project dedicated to making Linux user-friendly enough to be used as a mainstream desktop OS, and it's arguably the most successful iteration toward that objective to date. Ubuntu supports Intel/AMD PC hardware as well as Power PC Macs.

Does Ubuntu Linux make any sense for Macintosh users?