To expand that ... the i3 / i5 have the GPU and CPU together on the die ... so the power use compared to the T9600 needs to take into account the fact that you have to add whatever GPU (graphics processor) is going into the laptop.
Once you add them together you can see that the i3/ i5 and particularly the lower power models are real power savers ... compared to the old core2 processors.
Plus the newer processors have much lower idle power, and are more efficient (use fewer clock cycles to get the job done) ... we call that IPC (instructions per Clock).
I hope this helps explain things a bit better for you.
Mind you, you will pay a premium for the newer i3 / i5 laptops ... but the payoffs may be just what your looking for in terms of using it away from the power point.
"To expand that ... the i3 / i5 have the GPU and CPU together on the die ... so the power use compared to the T9600 needs to take into account the fact that you have to add whatever GPU (graphics processor) is going into the laptop. "
The Core I3 and Core I5 have an integrated memory controller which eliminates the Front Side Bus (FSB) and due to this saves approximately 10 watts of power. Due to the nature of this design, memory bandwidth is improved, as is latency for memory access.
Edit: Sorry, my bad. The Core I5 does have an onboard GPU. I have edited my statement. Reynod is right.
It would be wise to go with a Core iX model vs the C2D. It should save you time especially with turbo mode.
Depending on the type of database you are using and mapping software, it may even be wise to go with a mobile quad core I7 if the programs you use take advantage of more cores.