I'm thinking of installing Ubuntu PPC onto my old PowerBook - I don't think I'd get too much for it if I sold it now as it's pretty old so I figure it's worth more to me to keep as a portable device then the cash it would bring in. Why switch to Ubuntu? Well I'm a bit worried about the state of security updates for Leopard (which as you probably know is the end of the road for PPC Macs). Apple haven't come outright and said they're stopping support or anything like that but during the recent Diginotar cert debacle they only issued updates to Snow Leopard and Lion. In that particular case it was simple enough for me to manually revoke the certs (and I use Firefox as a web browser anyway which includes its own root certs) from Leopard's keychain but what happens when the next vulnerability is discovered? It may be something that I can't so easily fix myself.
So Ubuntu it is - I'll wait until 11.10 is released next month and then I'll divvy up the hard disk so I can dual boot. If I find Apple still releases updates for a while (there was a security update not too long ago so all is not lost!) I'll keep dual booting it - otherwise if it looks like the end of the road I'll delete OS X and go completely Ubuntu where I know I'll get updates for a few years to come.
Of course since getting the TouchPad I hardly even boot this laptop anymore so most likely it'll sit unused no matter what OS is installed...