I had just used the compare on the Canon website to determine which camera I wanted, and it ended up that the SD800 and SD870 had the optical equivalent of 28-105 mm (as opposed to the 35-105 mm equivalent of most - which gives me a bit of a wideangle).
I had just assumed that it was the higher megapixel version of my previous camera, but it's actually got some significant differences:
- It doesn't have the selector wheel for mode. It's got a three-mode selector switch instead - with the modes being movie, scene, and auto. When you switch to the scene mode, you can select all the other modes using the menu. This seems like an improvement to me, since I know I didn't use most of those other options.
- Another UI improvement - there's a play button. Rather than using the mode selector switch. This is a huge improvement - you just push the button, and the camera will turn on to view images, or you can just click it after taking a shot. So much easier than fumbling with the mode selector.
- It's got a bigger screen (3 inch vs. 2.5 inch) - another plus.
- It doesn't have an optical viewfinder - a negative.
- The body feels a little less sturdy. It's got a bit more plastic, which is slightly disappointing