Just Copied this from e Photozine. It seems that the apparent problem with the K10D is not exclusive to PENTAX:

Hi, I have had terrible problems with chronic lining/banding appearing on images across all isos.

I sent my camera back to Canon U.K. 3 tmes each time coming back with same problem. Tried different lenes, flash cards etc but no improvement.

As a result I borrowed a camera from my local canon agent in Ireland, tested it, straight away same problem. Only constant between my camera and this one was flash. So rented a 580ex, to go shoot wedding, same problem in the church, I was fit to scream!

I would rate 5d as an unusable camera for the professional. Also Canon U.K. and Canon U.S.A did not appear to know about this problem. I like others had to find out about it on internet. This is a terrible camera and atrocious customer support from canon.

In short I have noticed this problem across various isos starting at 100, with different lenses, memory cards and flashes but indoor shots in mixed light very susceptible to this banding.

The shop I bought it from, B&H Photovideo, would not entertain replacement or refund even though camera was sold in this state and I have repair record to show this. In fact customer service agents very unhelpful there, to the point of rudeness.

What are we poor saps who shelled out a fair whack of cash on these rubbish cameras to do?

see this link for other people who had same issue:
http://www.dslrphoto.com/2006/02/23/chuck-westfall-comments-on-5d-camera-banding-issues/

Banding is a loss of colour information which is usually the result of a lot of editing and saving of a 8 bit jpeg. image.

Have you looked at the histogram of these photos with banding to determine whether you can see lost colour information?

Ronnoco

Banding is a loss of colour information which is usually the result of a lot of editing and saving of a 8 bit jpeg. image.

Have you looked at the histogram of these photos with banding to determine whether you can see lost colour information?

Ronnoco

It is not me with the problem. I just posted this from e Photzine...I use the Pentax K10D's.

I suspect this is a problem with most chips, when they're pushed too far. More pixel density will exaggerate the problem.

The solution is to use a sensor with fewer pixels spread out more, or a bigger sensor. Thus there really is a reason for medium format digital.