[superdude]

Safari is multi-process and it has the best battery life.

[justsid]

Safari makes use of a kernel feature that allows giving some leeway for when the process should be woken up again (eg. from a timer source). That way the kernel can put the CPU to sleep until it can schedule as many processes as possible at once to wake up and perform their work. That way the CPU doesn’t have to wake up all the time to wake up a single process and let it do its work.

[mmebane]

Windows and Linux should be able to do that, too [1] - any idea if Chrome or Firefox make use of it?

[1]: http://en.wikipedia.org/wiki/Timer_coalescing

[Alphasite_]

It is a bit of a memory hog as well, but yes, it's battery life is just fantastic.