Image quality from the Pentax K-x was generally superb. The sharp lens helps immensely, but we also saw accurate, vibrant colours and generally low noise.
The K-x's ISO range can be pushed to the equivalent of 6400. Noise is definitely a factor at this setting, but we found if we kept the shutter speed as fast as possible we were able to get reasonable shots nonetheless.
Shots taken at ISO 3200 were excellent. There was some evidence of the K-x's noise reduction algorithm's stepping in and producing a little over-sharpening, but bumping up the ISO is by no means a last resort.
The K-x also has a slight numerical advantage over other mid-range cameras. Most mid-range DSLRs - the Canon 500D, Nikon D5000 and Sony A200 and A330 for instance - have a maximum shutter speed of 1/4000th.
The maximum shutter speed of the K-x is two-thirds of a stop faster at 1/6000th. This extra speed isn't much use on its own, but if you plan on buying particularly bright lenses it could come into its own for shallow depth-of-field jobs.
The only slight disadvantage the K-x has in feature terms is the lack of white balance bracketing, which is a fairly standard inclusion of a camera of this price.