And then she said...
...Debian. Lubuntu 12.04 is fine I guess, but Debian pure simple and true is where its at. Lubuntu is based on Debian,its just 'buntu with a LXDE interface. So why not just go for the gold from day one and Install Debian with LXDE? If you have fingers, can type and an IQ larger than your shoe size you too can configure Debian. PPCluddites guide is very helpful though.
MintPPC appears to be a dead or at least run over and dying distro. Forum has been down for a week or more now. And, MintPPC is just Debian with the Mint art-fart anyway, so, again, why not go for the gold from day one.
Don't expect Linux to be OS X. Its not nearly as polished, and tux won't hold your hand and kiss you nicely on the cheek whilst stroking your bum like OS X does. But in return for learning some (quite) simple stuff, you get a OS for your ibook that won't be abandoned on a church door stoop like a bastard infant anytime soon. I mean, Debian still supports Sparc for god's sake.
Gentoo and Fedora also still support PPC (but are like third tier builds), but have steep steep learning curves. Plus, Debian has a really simple package managment system, ka-thousands of apps, and is officially supported, unlike the 'buntus.
Her name was Deb. His name was Ian. Get it? Deb-Ian. Let it power your PowerPC.