Most of the benchmarks posted show them pretty close to each other in real world tasks and games. For comparisson, my neighbor has an older MBP with the 1600 and I have one of the Unibody MB with the 9400. We tried some games out to compare the two and we were pretty much dead even on fps in BF2 but this was at native res and the MBP is a higher native res. At 1280x800 we were still almost identical in performance on L4D and WoW (those are the only titles we compared).
It was weird though because, depending on the task the Unibody MB would beat the MBP. Using QT Pro to transcode some vid files into MP4 the Unibody MB was faster - Noticably faster. I'm guessing this is due to the GPU acceleration in QT that is Nvidia only currently... is that right? If so, that is a significant benefit to the Unibody MB over the older MBP assuming you might be doing any encodes and the new MB's have the benefit of the newer chasis/lighter weight as well. The MBP has some other obvious benefits such as FireWire and the larger screen though.
Really, I don't think you can go wrong with either; it's just a trade off of features so pick the one that best fits your usage.