Some folks on the MSI Wind forums are reporting a huge increase in battery life for hacktintosh netbooks after upgrading to 10.5.7. Why would Apple care about power management on Atom-based hardware? Dunno!
Of course, this could be a symptom of wider software optimizations or just a false alarm altogether. If it's true though, this is great news—aside from a few awkward interface difficulties, diminished battery life is (or was) the best argument against giving OS X a try on your netbook.