I trade with an off-the-shelf laptop, for various reasons. After years of playing with monitor heads and fancy arrays, I simplified my system into one that needs only a laptop. No monitors, no software that eats up CPU time or RAM. I got tired of having to take vacations without trading, thereby losing out. Vacations + regret = crappy vacation.
Caveat: I do not sit and bug my eyes out at monitors all day long. If I had to do this on a laptop, I would be wearing glasses by now. I don't.
It doesn't hurt that I used to write databases, but the magic of trading on a laptop is in the trader's ability to simplify their system to the point he is no longer hand-cuffed to an office, in order to trade. I suppose in a few years, more brokers will make platforms for 3G+ handheld devices, and I would be among the first in line.
However, if you're not there yet, and you still rely on gobs of indicators, charts, overpriced monitor array software, dozens of distinct symbols and news feeds, then a laptop would be a foolish choice, as all of those little tiny windows squeezed into a 15" screen would be impossible to use, plus your video card would be overloaded, especially with an extrnal monitor plugged into your laptop.
Don't get me wrong, I've seen the thread with photos of workstations. They're pretty. I just think they are better used for Flight Simulator, than for trading.