I know it get's maligned in other circles, but in tandem with UniWB, I think the IP feature is really incredibly useful... and much faster and more efficient than either chimping repeatedly or using live view to set exposure.
If you're like me and enjoy setting a manual exposure as often as is possible, I just love the ability to snap a shot, tweak the IP, and then go to town. And I don't have to do the shoot.... chimp... shoot... chimp... shoot routine if I didn't bring a light meter.
Here are a couple high contrast snapshots I took (out the car window) while sitting in my car, waiting to pick my daughter up from her school. Good time to fiddle with the new camera. Scene had lots of highlight tones... so I set my aperture, guestimated the shutter, set WB to Uni, then adjusted the Int. Preview, and VIOLA... no burnt highlights (well, I did let the green channel go EVER so slightly in the second shot).
cool feature (even if the shots aren't):
Anyone else find IP amazingly handy?