The wife and I are stalwart Pentax K-5 users, but we find that other cameras that perform just as well (except as very high ISO), and weigh less:
The NEX-5N with a Zeiss 1.8/24 on, is my favourite just now, a camera system weighing in about a pound (half a kilogram), and it does excellent panormas, even with the camera vertical! Add the Sony E16 lens to the package, and you have a complete APS-C camera setup that weighs just a little more, with a quality that astounds me again, and again. With a cheap K Mount adapter we've tried some Pentax FA lenses, and a very old Pentax-M 400mm (and a 2X converter), with impressive results.
My wife has just the E18-200 zoom on her 5N, which is an amazing lens: Not the fastest out of the blocks, but sharp from one end to the other. It was designed for the pro NEX movie cameras, and she is very pleased with it - seems the 5N and that lens together produces an amazing percentage of hits, focus almost always spot on, although, occasionally, the camera chooses a too low shutter speed for perfect results.
But the NEX-5N isn't rugged, and not intended for abuse, like the OM-D hopefully is (if we can believe the advertising guys it will be). Nor is the NEX-5N very discreet, as its shutter is LOUD! And the viewfinder is VERY hard to find (I searched the globe till I found one, but I haven't found a second for my wife). The excellent Zeiss 1.8/24 is sold out, for months to come, according to Steve Huff. Only problem I have with the Zeiss is that it doesn't come with anti-shake (nor does the E16), so you have to keep your shutter speed in mind!
But there is another rugged guy on the block, weighing about a kilo, with three lenses, two of which by SLR Gear.com pronounced as among the better there are, for any size of camera (the third haven't been tested, yet).
It is small & quiet, and with an adapter you can use any Nikon lens you can imagine on it (with auto-focus and anti-shake fully functional, in most cases), and it has already proved popular with the long lens guys - seen birds being photographed with 300-600mm zooms (that, in FX/FF terms, means 810-1620mm - to that you can add a converter, or two - the sky is the limit!), with excellent results, as long as you're VERY steady!
I gave one of these marvels to my wife, but she has since opted for the OM-D.
I'm talking about the magnesium-bodied, fairly heavy (half a serious DSLR in weight), supersmooth Nikon V1. This camera, with a screw-on Canon 250D close-up lens (you need a stepping ring, of course), is a complete camera system, covering everything but the very wide (the 10/2.8 prime is very much a 'normal' lens and there isn't anything wider, yet). Adding a TF1 adapter you can use (almost) any Nikon lens you can think of on the V1, and the results can be amazing - I've just tried a few lenses (as I wrote, I'm a Pentax guy), like the old 80-200/4 that Ken rockwell calls the sharpest tele zoom Nikon ever have made! Like this picture: