I chose the K-x over the K7 because of its low light performance(being half the price helps as well). I have read reveiws that state the K7 performs slightly worse than the k20 at high ISO levels. Being an owner of a k20, I can state that the K-x far out performs the k20 at ISO 1600 ( check it on the video review:
Videoclips about Pentax K-x Digital Camera ) . This camera is perfect for shooting pictures of people and settings where a flash would be considered intrusive. Its relatively fast focus speeds and hd video make this camera the perfect tool for capturing those special moments with my friends and family. I think you can get more candid shots when you don't have a flash announcing that a camera is present. I still prefer my k20 for more formal photograpy where a "hands on" approach is desired, but for everyday use, and at this price, I think the k-x is hard to beat.