After loading the new kernel, my laptop fan ran constantly, with disastrous consequences for battery life.

Passing these commands to the kernel fixed it:
GRUB_CMDLINE_LINUX_DEFAULT="text i915.modeset=1 i915.i915_enable_rc6=1 i915.lvds_downclock=1 i915.i915_enable_fbc=1 pcie_aspm=force"
Powertop estimates of power consumption improved from 14w to 8w.

Note that these power-saving options were disabled in newer kernels due to the risk of system instability. So far I haven't seen any problems, but don't blame me if you do
See here for more info

Hardware: Toshiba Portege R830, Core i5 2520M, Intel GMA 3000. The best BT laptop I've used.