I've heard that Canon changed the design of their SD line post SD400. The SD450, SD600, SD630, & SD550 all are SUPPOSED to have the redesigned, stronger screen design. I can't find any actual documentation on that, but I've read it on dpreview and other forums like it.

I now am using the SD600, and love it. Bought it from Costco in case I ever need/want to return it...

- Jon