People are reading too much into those machine IDs. We all know that the PB G5 will debut sooner or later. But not yet! The existence of those machine IDs only means that Apple is working on a new PB series which might or might not feature a G5. Regardless of the CPU, they have to test new computers and therefore need to run the OS on those machines thus the support for those new PBs in 10.3.5. Even if the new PBs were announced at Paris Expo, I'm pretty sure they would run a more recent build of 10.3.5. Secondly, due to the yield problems IBM is still having, it wouldn't make sense to release an iMac G5 and PB G5 at the same time. This would only result in a huge desaster for Apple. Demand for those new products would be so incredibly high that Apple could sell only small quantities of iMacs, PBs, Xserves and PMs resulting in an enormous back-log. In a nutshell, regardless of the heat problems, we won't see a PB G5 for some time. After all, the current line-up is still selling well, so Apple is no rush to release a PB G5 just for the sake of it.