With laptops the trade-off is usually battery life vs processing power.
Unless you are doing a lot of high level graphics processing (or EXTREMELY high level math), I'd lean towards the battery life side of the equation.
Do you need video out?
SD slot is almost assumed present.
USB? probably the same, but actually starting to be absent from some smaller units.
Hardwiired network connection?
"N" spec wireless? Nice if free, but necessary??
The one I'm using now is almost 3 years old Centrino Duo 2.2 GHz with 2 GB RAM.
I run Photoshop, Visio, sometimes a little AutoCAD, multiple instances (12 or more) of Excell, multiple instances of Word and RTF docs, sometimes two browsers with 10 pages open each, (sometimes all at the same time) and I leave it on (allowing it to sleep after an hour, or when I close the lid) all week without a reboot.
It does just fine.