I would go with the netbook. I think most of us here love the 12" PB, it was the best notebook Apple has ever made. But, the 867MHz PB is 6 years old now and with SL coming in September, PowerPC is going to be extinct and new programs are going to be made with Intel in mind. I love the old PowerPC and everything, and I was very tempted to get a Quad G5 (posted in Mac Pro/PowerMac forum) but an Intel is the future, not PPC. It will be missed, and if a 12" PB comes along in my time for cheap or free, there is no doubt that I would not take it.
Its amazing how fast technology moves now-a-days, I feel like it was yesterday when Apple released the PowerMac G5...