The wife and I are stalwart Pentax K-5 users, but we have found that other, non-Pentax, cameras can perform just as well (except as very high ISO), and, yet, weigh less:
The NEX-5N with a Zeiss 1.8/24 on, is my favourite just now, a complete camera system weighing in at about a pound (half a kilogram), and it does excellent panormas, even with the camera vertical - just now my outdoor favourite camera system! Add the two-ounce 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 (often better results than when I've used the same lens on the K-5).
My wife has just the E18-200 zoom on her 5N, which is an truely 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, but works perfectly on any NEX, and she is very pleased with hers - 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. A monopod is a perfect add-on!
But the NEX-5N isn't what I'd call rugged, and nor is it intended for abuse, like the OM-D hopefully is (if we can believe the advertising guys shots of one being soaked in rain). Nor is the NEX-5N very discreet, as its shutter is LOUD - far louder than the K-5, for instance!
And if you are a person that likes to use a viewfinder, it 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! The Sony 18-55 kit lens is OK, but I seldom use mine (it is stowed away with a few other kit lenses, that I've managed to acquire through the years).
But there is now another, very rugged, guy on the block, weighing in at about a kilo, with a flash & 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 their auto-focus and anti-shake fully functional, in most cases - need to have their own focusing motor), 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. So now I a very happy punter, indeed!
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 (including decent macro) 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 and you can use (almost - see above) any Nikon lens you can think of on the V1. The results can be amazing - I've just tried a few AF-S lenses (as I wrote, I'm a Pentax guy), and the old 80-200/4 that Ken Rockwell calls the sharpest tele zoom Nikon ever have made! The results have been more than OK, like this picture: