I am also wondering the same thing, whether they feel hot or not when using on a lap (for both the 9400M and 9600M GT situations).
Also I'm curious about the actual temperatures of the internals. Anybody got BootCamp already and care doing an HWMonitor check (sorry I'm new to Macs so I don't know if a similar took is available for OS X)?
I had the 6 month old MBP 2.4 and "upgraded" (yeah LOVE the new style, I hated the old fashioned keys on the old one)... the new one is awsome. The new one isn't COOL, but it's able to be used on the lap, does a much better job distributing the heat elsewhere I suppose. If you're taxing the processor\video GPU it's not "comfortable" but it's not unbearable like the pre-revision models.
Like all other MBP's and PB's: at full tilt, closing the lid for a few minutes preserves enough heat to allow the cooking of delicious directly over the Apple logo.