One odd quirk is that I think the S230 actaully has more movie ability than advertized on the S400.
Over the years, personally I've gone from Elph(APS film) -> S100 -> S230 and couldn't be happier. (but the S400 has more megapixels, and I think 1x more optical zoom)
Great cameras. Oh and while few ppl would need it, the underwater case for the S230 is absolutely top-notch.. I'm a design engineer and it still impresses me every time I use it.
Cheers,
Mike