UPDATE: See the Photoshop CS5 version here.
Ok, so if you haven't seen the new Content Ware Fill feature in CS5 yet check it out here. I was looking into it and got a link to a GIMP plugin called Resynthesizer. I decided to play around with it a bit and will compare the same edits in CS5 once its out. Here are the two tests I did, the first was some small edits to remove a duck, some waves, and the power lines(and shadows). The second was a larger edit to remove a big tree witch didn't go as well.