Our friends over at PCPerspective have taken a Core 2 Duo T7400 "Merom" processor and installed it into a Dell XPS M1710 notebook. They had to contend with a couple of performance related anomalies, but other than that everything seemed to work fine. It's possible that we'll see Core 2 Duo notebooks very soon because the new chips can drop right into existing designs.
"One of the nice things about the XPS M1710 is the relative ease at which you can disassemble it to upgrade the CPU. I will not do a step-by-step procedure since anyone willing to tinker with the innards of a laptop can generally figure this stuff out without me telling them. However, just so you have an idea, you unscrew bolts from the base of the laptop, detach the display and cables, and remove the casing."