When I was using a PowerPC-based computer (Mac), one of the Linux distributions that I always have with me is YellowDog Linux. This was until the PowerPC Ubuntu distribution came along, of course. AFAIK, Ubuntu stopped developing for the PPC architecture anymore but I may be wrong. Not to worry, though, because I found another Linux distribution for the PowerPC and this time it is based on Slackware. Cleverly named Slaskintosh 12, this new version comes with updated packages such as KDE 3.5.7 and GCC 4, among others.
So, if you have an old PowerPC-based Mac, then maybe this is a good alternative to buying the upcoming Leopard OS.
[image from Slackintosh site]