Pros:
Low light: This is a camera that takes great low light pictures, you can push the ISO up pretty high and still get great pictures. This was the biggest reason for me to upgrade. I had a hard time taking pictures of my kids in various performances with terrible lighting conditions. Obviously one needs a good lens. But with my old camera I had to throw too many away. This camera combined with the DA 50-135mm lens is one terrific package (see it on the video review:
Videoclips about Pentax K-5 Digital Camera ) for such situations.
Weight/Size: this is the most compact camera at such a level that you will find.
Weather resistant: This is a weather resistant camera! Combine this with a weather resistant lens and you are all set.
Electronic Level: I thought this was a gimmick but after using it for a few days, I find it indispensable to take level photos.
User Selectable Focus points: these are standard in expensive cameras, nothing special if you have used such cameras before but for somone upgrading I quickly found out how convenient this was.
Shake reduction: Pentax unlike Nikon/Canon has shake reduction built into the camera, so any lens you put on it has shake reduction function.
Lenses: Pentax has small pancake lenses called limited lenses. Try these if you are new to Pentax. They are superb and great to walk around with without looking like a dork.
Cons: Expensive...