Damn!
It looks like I'm going to have to give up on my test: the IS on the 17-55f2.8 is apparently dying on me
I am having trouble getting sharp images with the combo and the IS is emitting "cracking" noises while the image wobbles in the VF from time to time.
I asked a Canonist friend and he told me that this is not supposed to be like that: defective unit.
I still took a few pictures with IS off but since the lens is defective, it's pretty much inconclusive (loads of CA wide open, not so sharp... not really what I had hopped for...).
Sooooo, I have basically nothing to offer, except the confirmation that K10's built quality is nothing short of exceptional and has really set a new standard for this class of camera.
Also the AF speed on the 30D didn't particularly amaze me, except in low light where it would either focus faster than the K10... or not at all. Again, this may be due to the defective lens but it doesn't change when IS is turned off.
In good light, both are really fast, too fast to tell them apart IMHO.
As far as VF are concerned, the K10 is better but not by a mile, the 30D is OK and I agree that having AF sensor marks permanently in VF is a good thing.
One thing I like on the 30D is the back wheel: I dream of a Pentax keeping the two upper wheels (front and back) and adding a concentric wheel around the directional pad customizable at will (ISO, AF points, metering mode, WB, AE compensation...).
I really don't like the "one button=two parameters" (ex: drive with front wheel, WB with back) but that's part of Canon's philosophy and maybe I just need some time to adapt to it.
It took me a while to find the DoF preview button, until I remembered the old days of my very first SLR (a Canon AE1) and looked at the front left of the camera: there it is! Still at the same (strange) place
On the IQ front, well, I think the 30D sets the reference for high ISO quality: ISO1600 is really clean and ISO 3200 useable. I'd say about 1 stop better than K10.
One funny (?) thing is that I could find obvious traces of HPN (Horizontal Patern Noise) in the shadows of the Canon high ISO images: not really a problem but it's there... to me it's about the same magnitude than VPN is on the K10 (ie very faint) and doesn't really appear until you push the enveloppe 1 or two stops.
OK, I think I'll stop here, I haven't got the impression of having reavealed anything new but I had back luck with the lens. I'll try to get another one that works next time.