It's great to hear this is an active area of development, as it's probably the biggest remaining factor in me choosing host OS.
This is a case with my new Dell Precision M6600. It have on-chip GPU and discrete GPU. I still trying to find a way to switch to integrated GPU. And this one of the areas Ubuntu 12.04 should fix (well. To be exact, not Ubuntu, but kernel included into this distribution).
Just from witching from external GPU to internal GPU I expect to bump battery-time to ~6 hours from current 3 hours.
Windows 7, pre-installed on the machine - 4 hours, 30 minutes
Ubuntu 11.10, dual-booted on the hard drive - 1 hour, 48 minutes
Ubuntu 12.04 alpha, booted off of a USB stick - 1 hour, 38 minutes