I currently use an Olympus E-P2 as my walkaround/travel camera, and agree with David about the Panasonic 20mm f/1.7 pancake which is on that body 80% of the time. I'm anxiously awaiting the NEX-7 now - the larger sensor will be a plus and my main annoyances with the EP-2 are its horribly slow responsiveness and marginal low-light/high-ISO noise performance.
No way this will replace my DSLR gear (Nikon) but for a lot of what I do, I'm just not going to lug around a D3 and big lens, nor is the iPhone quite up to snuff. I can't see going back to a P&S either. The mirrorless "EVIL" stuff is just the ticket and I have some nice M-mount lenses I can use on the E-P2 or NEX-7 with adapters as well.
You've gotta admit this is a cool looking, and impressive little camera...
Olympus E-P2 by
cjcam, on Flickr
but it sure can't replace the bazooka for racing or wildlife...
Rest break at Laguna Seca by
cjcam, on Flickr