Dont bother about CPU temperature, everything below 105 degrees Celsius is ok, i have i7 15" MBP for about a week and its normal for that kind of processor. The new Intel architecture is really cool in idle state, but it gets hotter than C2D CPUs, in every i3, i5, i7 mobile computer.
back to the problem... its propabbly u bug in temperature readings, or just fan speed difference during bootup process. Im just guessing, but when you first boot, the CPU gets loaded with bootup process, after second reboot, the fans are running higher speed (because they adapted to the earlier temperature state), but the cpu isnt too loaded during shutdown and reboot (especially on the grey screen etc), so it can cool down the cpu and the heatsink. What Im trying to say is that the cpu during reboot has got much more time to cool down with help of the faster fans.
