I have a Canon IXUS 80 IS, which is detected as PTP by digikam. I can use digikam to access the pictures. However I prefer the mounted folder view. This was working properly under KDE3.5. With KDE4 (both under Sid and Karmic) it does not. What happened?

Well, you need to mount it as an USB device then, not with PTP. Change the setting on the camera to USB, when you plug it in it will appear in the Device Notifier widget.

Works fine here with a Nikon D50, KDE 4.3.4, digiKam 1.0.0-beta5 on Kubuntu 9.10

I think this is not possible. My camera does not offer such an option.
Besides, the same camera (without changing anything) works fine under Hardy with KDE 3.5.

Open Konqueror, and type in "camera:/"

Problems like this is why run a base Ubuntu and select KDE apps I like to install and run.

Cannon Powershot shows up just fine with Nautilus however will not show up in Dolphin or download images with DigiKam. The above solutions are not working for me. Does anyone else have a solution to have Digikam download the images directly?

Digikam works fine in this regard ( it worked fine well over a year ago in fact ) at least on my systems running SUSE. ( 11.0 - 11.2 )