I noticed the dark splotch in the upper right hand corner in a shot from the weekend with a clear blue sky. At first I thought it was maybe just a puff of cloud or smoke that I hadn't noticed in the scene. Then today I took some shots with a lot of sky in them such as this one and the splotch is there again. It's subtle and you might think it's just a jpeg artifact or dust spot or something, or you might not even notice it if I didn't point it out, but it's unacceptable to me. I am returning the camera. It's a little more obvious in this shot oriented vertically, it's in the left top edge of the frame.
Oddly, it doesn't appear in every shot, so I don't know if it's the focal length or the angle of the light source or what. It should appear in this one (from a few days ago) but doesn't, while other similar shots have it:
I bought this camera refurbished from canon direct. Don't know if that has anything to do with it, but I still intend to replace it with another G15. A new one. And then test it thoroughly.
UPDATE: Returned defective copy, replaced with new one. Tested, no problems.