As promised, today ends my week with just the PowerBook. I really had no problems apart from YouTube. Firefox is slow, but usable. Dillo is lightning fast, but lacks Javascript support, so banking sites and JSTOR wouldn't work. It's still great for everything else. I wrote a long paper using Abiword which went fine. PDFs were handled by xpdf. I haven't found a PDF reader that's lighter and faster.
My biggest complaints are the trackpad and the GPU, neither of which would be a problem in OS X. I never liked one button trackpads, and this one is no exception because it lacks scrolling and right click functionality. I used a USB mouse after the first few hours rather than try to get it working. As expected, the nv driver lacks acceleration and is generally really bad, which reinforces my desire to never use NVIDIA hardware whenever possible. I think the T42 is faster for browsing just due to direct rendering on the Radeon 7500.
Overall it was pretty good. It was perfectly stable and I was able to do just about everything I needed to do.