Without hibernating to disk first?

or via using the Ultrabay as secondary battery? [1]

[1] http://www.thinkwiki.org/wiki/How_to_use_Ultrabay_batteries#...

[EDIT] Also I'm not in any way affiliated with IBM/Lenovo. But the always-on USB-port feature is also a handy emergency travel phone charger if you can (or have to) prioritize phone usage over computer usage with no power outlets in reach. Since the Ultrabook is off and doesn't have to use any power itself you could theoretically stay connected for weeks given a charged battery pack.

Ultrabay as secondary battery. I had two batteries in the machine always. One 9-cell in the machine, one 9-cell in my bag and a 3-cell in the ultra bay. I could get 9 hours out of that without too much trouble and both the 9-cell packs were knackered.

Now you can get 22 hours apparently on a X220 with battery base and a 9 cell!

I use my ThinkPad as a charger too. You have to turn it on in the BIOS but it charges literally anything.

Great. So why can't you do it on a MacBook Pro?

Because they valued more the engineering advantage of a built-in battery: thinness, weight, individually connected cells for power management.

Those attributes of design are more appealing to the majority than are interchangeable batteries.

My MBP and MBAir, even with the single built-in battery, gets more runtime than a 1996 laptop with two battery packs.

Because removable batteries would offend the sensibilities of most Apple customers?