This isn't at all confirmed or verified, but it seems that loading up an otherwise Windows-equipped netbook with Mac OS X can boost the battery life on the little computer by up to 33%.

User Dalton63841 from the MSI Wind Forums decided to toss Mac OS X 10.5.7 onto his MSI Wind, one of the more popular netbooks for Hackintosh purposes. Under the Windows environment, the Wind was able to run for about 3:45 using the provided six-cell 4400mAh battery. Switching to a Mac environment, the same netbook was able to get "a shade over five hours."