Yes, Ubuntu on PPC can be a great experience, but then you realise that 75% of the applications aren't there. Although it does make these old machines more modern, you soon run into a lot of the same problems. Incomplete video card driver support for "quartz" acceleration as on OS X with certain cards and the lack of flash support. The later is not much of an issue thanks to HTML5 support.
The biggest issue really is that you're an outcast anyway by buying into the Linux Desktop Environment, and your a leper in an outcast community by running PPC. You're left among a community that is maintaining support for games consoles running Linux on PPC architecture and the ever dwindling number of IBM servers that are running off the Power architecture.
None the less it's the only modern and secure platform for PPC computers that is readily updated in 2014.
The biggest issue really is that you're an outcast anyway by buying into the Linux Desktop Environment, and your a leper in an outcast community by running PPC. You're left among a community that is maintaining support for games consoles running Linux on PPC architecture and the ever dwindling number of IBM servers that are running off the Power architecture.
None the less it's the only modern and secure platform for PPC computers that is readily updated in 2014.