Although it seems to be working well in my recording tests, I'm not really convinced that a laptop-based solution is going to be appropriate for playing live. For one thing, I think the laptop gives the wrong impression--that I'm triggering samples, or that it's setting up my loops for me. With stompboxes and their relatively crude interface of footswitches and knobs, the theatricality of the live performance is preserved, which was a large part of the motivation for my pretentious solo project in the first place. Besides: dork with the laptop.
In any case, I'm surprised that there seem to be very few devoted audio notebook builders, other than Rain Recording's LiveBook or NUSYSTEMS in the UK. Alienware also makes a desktop chip-based "pro audio" laptop, but I'm guessing that's a bit hotter and high-power-consumption than I would want to work around. Beyond that, you're left with the usual suspects: MacBook, Lenovo Thinkpad, Sony Vaio, or other general-purpose machines.
I've been trying to think about what I would want in a live-rig laptop. I feel like there are two basic priorities: latency and durability. Screen size isn't critical for my needs, battery life would be nice (although clean power is more important), and the keyboard obviously wouldn't see much use. A huge factor for latency would be the interface--and here's where I think it's interesting that laptop audio hasn't really advanced past the Soundblaster days. Video output has become increasingly sophisticated, with upgradeable 3D cards and different ports, but it would take a miracle to find a laptop that could handle high-Z inputs (which are compatible with the load resistance of guitar pickups). Still, that's what USB interfaces are for, even if they add bulk and complexity.
I'm sure that if you have roadies and money for backups, it's worth taking a laptop into a rock situation. But I've never played that kind of crowd--I've played coffeeshops and seedy college bars. I worry about pulling it off the stand by the instrument cable, or some drunk spilling a drink all over it (the Lenovo's Thinkpad keyboard actually incorporates drains for liquid, which might help). Especially for non-DJ musicians, where audience members sometimes wander onstage and mess with the instrumentation, there are a lot of unpredictable factors to consider. No, I think I'm better off with dedicated pedals for live work. I'm tempted to reconsider when I have some money sitting around--but until someone offers an integrated pro-level audio interface in a durable shell (to make the whole package as simple as my stompboxes), the cash is better spent on analog hardware or a new bass.