I’ve been trying out the MacBook on both dual and single core mode. With the help of CoreDuoTemp Utility and Apple’s Developer Tools, I have found that it will always run at full processor speed of 2 GHz when you use the processor in single core mode. On the other hand under dual core mode it will generally run at 1.5 GHz, occasionally dropping to 1.333 GHz.
Even while it is compiling fink in the background, the processor is mostly running at 1.5 or 1.83 GHz in the lower powered parts of the compiler, slower than the 2 GHz max per core.
I do think that the power management could be improved to allow the processor to SpeedStep down to the minimum 1 GHz. Maybe someday Apple will produce a firmware update that will do this.