I also have some issues with PPC. I have an eMac and the CD boots fine and the installer runs ok up to a point where I get the error message "An error has been detected while trying to use the specified Ubuntu archive mirror"

I used the ISO from http://cdimage.ubuntu.com/daily-live/current/ and downloaded the PPC ISO with a time stamp of "26-Apr-2011 00:04".

I tried also installing without the network - assuming it would just use the CD/DVD media to complete the install, but no cigar. It keeps getting stuck with the same error and each time you click the "Ok" button the screen just re-appears until you click about 20 odd times by which time the button has no more effect.

Any ideas?