i have a canon myself...SD630, and it's my baby! got it last yr and i loOOoOoove it! canons are amazing quality and are one of the best out there, if not THE best.
i don't know too much about cameras, but while i was shopping for mine...i looked around, and was debating over a canon or sony. they are at the top of the line, but a dude at Blacks (i think) told me that while canon and sony cameras take relatively same quality pics, the body of the canons are much better and sturdier. A lot of sony ones he said have quite a bit of plastic in their body, so they tend to be lighter and not as good quality as canon bodies. i've held sony's and canon's...and i do feel the difference in weight and canon's definitely feel better in quality. it's like a brick. really nice brick
so that's my opinion on canon cameras.
plus most of my friends who have shopped for cameras have canons and never regret getting a canon. one of my friends got a nice 3" touch screen sony a while ago and then wished she had gotten a canon after lookin at mine. hehe so
to canon!
u won't regret it! but i say get the SILVER version of ur SD870 IS! hate the black on silver! tacky!