I suspect my problem with this camera will be that it will leave f2.8 and get to f5.8 fairly quickly. I have a G11 but at Christmas, I borrowed my daughter's D7000 and stuck on my 17-55 f2.8 and shot with that -- because one thing I've found with inside daytime party photos is that f2.8 is hardly adequate except at higher ISOs, and f5.8 won't work at all. (Flash? Most people don't care to be blinded with repeated flashes during Christmas parties, and since nothing is posed, flash photos are not often attractive because of shadows and glare, etc.) The D7000 @ 3200 worked okay, but even then, the photos weren't what you'd call "bright."
I can see a camera like this being useful as a backup for trekkers, where you're outside most of the time and also have another system (or, if the shots are just intended as "casual" and you don't really need the flexibility of longer or shorter lenses.)
As for viewfinders...I have to agree with Slobodan. I have two Panny GX1s and I bought one accessory viewfinder to share between them, and shooting yesterday afternoon in bright sunlight, with a long lens on one and a short lens on the other, I found that half the time, I couldn't make out the screen on the one without the accessory viewfinder. It was driving me crazy. I've had a number of these top-end Canons P&S, and also a Nikon P7000, and now a fairly complete Panny system, and to tell the truth, it's often a relief to shoot with a regular DSLR with a good mirror viewfinder. ON the other hand, my full-sized system is a NIkon D3 (and a recently departed D300) and it's just too big, both body and lenses. My girlfriend has as K5 with five or six lenses, including the three pancakes, and I was shooting with that last night, and if there were about three more really good primes, that might be my ultimate solution. Or maybe the Fuji. I'ver heard good things about the viewfinder system there, although some of the reports on the glass aren't too encouraging, which is strange, because Fuji does have a reputation for good glass.
Be interesting if Pentax stayed with APS-C but managed to squeeze the size a bit more. The frontal area isn't bad, but the K5 is a chunky little thing.