aside from faster performance than the P4, it only consumes 25-ish watts of power and gets good battery life w/o overheating. The P4 consumes battery and gets extremely hot. (up to 140F in some cases!)
Personally I think you should look at the Turion 64 chip as well. Good battery life and performance plus 64-bit support for future proofing.
Maybe it's a stupid question, but...
I'm looking for a new laptop, but I'm not sure of the difference between Pentiums M and 4. I know that M is lighter and more effecient, but I can't figure out how the GHz compare. That is, a Pentium M 1.6 GHz seems to be a lot better then a Pentium 4 1.6 GHz. Can anyone clarify how I can compare the two based on the numbers?