The K10D sounds by all accounts like a fine tool. I wouldn't send it immediately back because people don't post about it.
Keep in mind that weather resistance doesn't mean "under water capable".
As for the in-body IS, which is becoming popular from those other than Canon or Nikon (IS in the lens is "better", especially for longer lenses, but does cost), it should work with ALL the current Pentax lenses, but may NOT work with older ones, with or without an adapter. The reason is the electronics between the lens and body. If the camera isn't allowed to tell what the focal length of the lens is, it can't compensate for camera shake. So, naturally, manual lenses won't work with IS.
Still, it isn't a Pentax limitation. It is the same with the new Olympus and others.
So open the package when it comes, read the manual (ha), and take some shots with an open mind. And post your examples here. I'm sure you'll get some good info to back up what you think of your new piece of equipment.
Enjoy...