I just got a K2000 (about the same size as the K-7 I think) specifically for use with a DA 40, for pretty much the type of use you are thinking of. It makes for a really small package, and the focal length is not all that far off of the old 50mm film camera "standard" lens.
I've had the 40 for a while now, and after only a few days of shooting with the K2000/DA40 combo I can say that the size and portability is really nice. My other camera is a K20D; the difference is noticeable. Hanging around my neck or shoulder it looks more like one of those "bridge" cameras than an SLR. It just disappears when held in the hand at your side.
Here are a few shots to give you a feel for the FOV of the 40, nothing really artistic, I was just out walking around to get a feel for the light weight body/focal length combo.
The other lens I can think of would be the DA 21, which is slightly bigger but a really nice "walking around" lens. I took most of the shots on my last 2-week trip with the DA 21, on the K20D.
Here's are 2 shots, first one with the DA 40, followed by the same shot with the DA 21, both taken with a K20D, just enough time between them to change lenses:
Now with the DA 21, from the same spot: