why i switched to external flash
I tried to compare the viewfinders. While they are similar enough in size to make it hard to tell, it seems like the 450D's viewfinder is a little bigger than the 300D's.
Meanwhile, the 450D's viewfinder is noticeably clearer — kind of like switching to a pentaprism (I don't have one on me to do a direct comparison, but this is just to describe the general character of the change) or from the kit lens to a 17-55mm f/2.8. Then again, it could just be my 300D's viewfinder is dirty. Or maybe it's the psychological effect of:
a) Canon claiming it's brighter
b) that lovely nine-point AF layout =)