The underwater housing looks pretty cool! I just bought my sd450 tonight! (battery is charging away as I type) I have a friend who bought the housing for his sd400 and said it works very well... Looks like the 450's housing is slightly different than the 400, so if I want to use on my upcoming trip to Maui, guess I'm gonna have to get that bad boy for myself!!
Also, still looking into a screen protector of some sort, preferably hard plastic, not the soft stick-on kind.