When I'm doing UI usability I usually just pull out a real iPad–the simulator is just there for "this change looks about right", and I coalesce a couple of these changes together before running on a real device. I rely heavily on AutoLayout, so most basic UI work is done on the iPhone simulator anyways; I only switch to iPad when I'm testing specific features such as split-screen support.

By the way, battery life on virtual machines has gotten better, I can get around 3-4 hours with a Windows VM running and seven or so with a lightweight Linux one. It seems like Windows has a penchant for preventing the VM from idling which really kills battery life.