"What's with all the laptops?"
I've gone all laptop for a few reasons.
Ergonomics: For 6'4" me, quite a ways off most ergonomics charts (in theory not, in practice yes), the best position I've found at home is in a reclining chair with the computer on my lap. It isn't recommended anywhere that I can see, but with the position I hold my computer in, all the actual ergonomic factors that you are supposed to seek out are in play: I'm usually partially reclined so it's more like I'm in a chaise longue, which I've seen mentioned as one ergonomic optimum in a few places (and I agree). My wrists are very straight and unpressured. I don't use the trackpad a lot anyhow and it's in easy reach. I can go all day like this no problem. (Yes, I am aware that I shouldn't even so and in practice don't. My point is that I can.) Very few desktop setups have been able to match this.
Also, Dvorak on my laptop keyboards has proved sufficient for me. YMMV.
Display Space: My laptop is at 1600x900 (yes, exactly). I'm in Linux running compviz, and with a single keystroke I can switch virtual desktops arbitrarily quickly. (With compviz now it can be literally a single frame on the display if you like; I find I prefer a bit more animation so my poor primitive lizard brain, already struggling with this whole "computer screen" thing, doesn't get completely disoriented.) I still like my dual-monitor display at work but I can't say it's critical.
In Windows, I would scream. Even Windows 7 is still too multi-desktop hostile for this to work.
Computational power: Usually my compilation is actually offloaded to fast VMs anyhow, so that's less of a problem. You shouldn't buy the cheapest laptop you can get, but anything above about $600 should scream for most dev tasks, even modestly-disk-intensive loads, because everything comes with such obscene amounts of RAM nowadays that a lot of stuff is hitting cache anyhow. With a full desktop Linux and two VMs generously allocated with RAM, I'm just barely using all 4GBs, including disk cache. (Without it, I'm at 1.8GB free RAM. Obscene, I tell you.) Anything else and laptops are fine. Admittedly, you may have to run Linux.
And this laptop is now coming up on a year old now, and there's been advancements even then. Just about the only thing I do now that shows any sort of delay is starting up Firefox, and, well, I'm still waiting to see the system that doesn't take visible time to do that :)
The last desktop advantage for dev is IO and I expect SSDs to end that disparity. (Leaving behind only 3D graphics, but unless you're developing a 3D game that shouldn't matter for dev.)