"Oh well I guess Linux on this thing is out of the question"
but why do you say this?
there is many linux distros with power pc support, pclinux is not one of them
the reason is that nobody likes power pc architecture anymore, not even apple, only one big company is using it, sony in the ps3 and ps4 afik won't use it anymore, this is why very few linux distros support it
about gpl software on mac, practically everything you have in linux is present on mac except for desktop specific apps but many others like gimp, pidgim, songbird, firefox, opera, libreoffice, vlc between others have a mac port