Go here http://www.flickr.com/photos/samfeinstein/476181737/ and look at the two frames labeled 18 mm and 24 mm. Click on "All Sizes." The 35 mm equivalents for these are shown in the parentheses – 27 mm and 36 mm. The two cameras you are looking at are 28 mm and 35 mm (35 mm equivalents) at their widest, so these two frames are almost an exact comparison between the two focal lengths you are asking about.

One thing to consider... The SD800-IS has a slightly wider angle lens, but the reviews say, "there is a slight, but noticeable drop off in sharpness towards the edges and corners in some circumstances." You might find that you zoom in that first step to avoid the soft focus on the edges and then you wouldn't have such a wide angle anyhow.

As long as you are looking at spending the money on an SD800-IS, how about getting an SD700-IS? The SD800-IS only zooms to an equivalent of 105 mm while the SD700-IS goes to 140 mm.

While I'm spending your money, maybe you can wait until you see the new SD850-IS on the shelves. It's an update on the super-popular SD700-IS. The 850 has the newer Digic III image processor with face detection and it's 8 MP instead of 6 or 7 MP. You know how to read these charts, I can tell, so look at this and see what other improvements there are. Be sure to note that the lens zooms to an equiv. 140 mm. The difference between 105 mm and 140 mm is MUCH more interesting to me than the difference between 28 mm and 35 mm.