5 months ago I transitioned from being a desktop C# app developer for medical devices to a Rails remote contractor.
This meant going from a dual quad core 3.33 extreme desktop machine with 3 displays (2 x 24 and 1 21) to an 11" Macbook Air with a 1.7 dual i5.
I'm much faster on the air. I have a tiling setup that I can quickly switch/move windows around, it keeps my vision and neck focused and reduces strain to both. It allows me to better mentally focus on what I'm currently working on, instead of having my IDE, source control, collab tool, bug tracker, etc, always visible at the same time. I'd rather do a couple quick chord commands than snap my neck 30 degrees one way for 15 seconds seconds then snap it back in the other direction.
As to heat/power? Spectacular with my MBA, this thing is as fast as last year's Macbook Pro and the iMac the year before. I've been writing software professionally since '96 and at least in the windows world, the tools have not changed a whole lot in that time period. The only advantage of a faster machine is faster compiles and db rebuilds/queries. And I'm not doing that enterprise level work of 300k+ code bases and 5 gig databases anywhere. But I did 15 years ago, and yeah, now something that would used to take over an hour might take 2 minutes. On my MBA is might take 5 minutes. For something I'd do a handful of times a day, not a big deal, but again, I don't do those types of things anymore.
Don't get me wrong. I'd appreciate more resolution. But probably more inclined to use that for extra clarity rather than increase my desktop space by a significant degree. There's a sweet spot where bad habits begin to creep back in, where just too much info is presented at one time that cognitive overload begins to set in. Just my personal experience, but I've had both setups and the latter works much better for me.