This puppy is bigger and heavier than my mirrored, w/ view finder Oly E-620, making the whole mirrorless design pointless.
It is big for a mirrorless camera, because unlike any other mirrorless interchangeble lens camera (MILC) on the market, it uses the same lenses as the mirrored DSLRs. The downside is that due to the rules of optics, the camera body still has to keep the lens a certain distance from the sensor, and so there's a full-size mirror box for a mirror that isn't there. That empty internal volume adds bulk. The benefit is that you're not stuck with a restrictive set of lenses with a specialty mount (like an Olympus PEN, a Nikon 1, or even Pentax's own Q). Instead you get to use any K-mount lens ever made, which provides nearly limitless possibilities. So, interestingly, Pentax makes both the smallest MILC (The Q) and the biggest one (The K-01) on the market today.
The reason your E-620 is smaller is that it's a Four-Thirds camera, with a smaller sensor. The K-01 has a full-size APS-C sensor, and APS-C cameras are always bigger than 4/3 bodies. Of course, the K-01 has the fantastic sensor shared by the K-5, and might be worth the extra bulk for certain shooters.
For me, personally, it's bulk I don't mind because I'm a big guy with big hands. Having a clunkier camera in my hand isn't bad. Trying to stow it in my jacket pocket on the other hand, even with the "pancake" 40mm lens, is a different story. Instead, I think of it as an unobtrusive addition to a small camera bag or backpack. I can actually carry two cameras in one smallish bag (with my K-7), and a single set of lenses that works on both.
I'm a big Pentax fan, but this camera is honestly not a good buy for someone just looking for a new MILC system. If you're trying to get a camera and a small set of glass from the ground up, there are better options from every manufacturer. But if you already have K-mount Pentax glass, the K-01 provides a great opportunity to have a second body with a smaller footprint, with a terrific sensor, at a cheap price. That's who this camera is really best for.