All depends on how mobile ya need to get, I guess.
Being a mad t/a bod (chartist) I like to be able to display charts with "reasonable" resolution.
My current mobile rig is a netbook, Lenovo S10, 10 inch screen with good enough resolution to display one or two charts overlaid on the IG trading platform.
Fits in a brief case or manbag with ease and Use use 3's wireless broadband with little hassle (city based).
Only problem is a need to carry a mouse as well as mouse pads n my fingers don't often agree.
Have sussed Sony's latest vaio with even a smaller footprint but same screen resolution and will prolly upgrade to that and a pair of reading glasses in time :)
Other good thing about the netbook/ very portable notebook concept is that you can whack on extra peripherals (mouse, extra monitor etc) if you have the opportunity.
Sad but true, I have as part of my quest for a mobile "trading desk" built a battery powered briefcase (contains 2 small 12 volt sealed lead acid batteries and a small inverter, all inside a standard briefcase, providing a 240 volt source) that gives me the ability to run an extra monitor for about 4 hours, so I can trade multi-screen from a park bench.
However... I have been known to suffer from Uber-geekness, and I am a hardware hacker/mad inventor at heart.
