If chiropractic limited itself to minor "adjustments" and such, it'd be okay, IMO. When I was 7 years old I twisted my neck and slipped a disc; the only guy open that late at night was a chiro, my mom took me to him, and he gave me a twist (scary!) The pain reduction was immediate, though not total.. it took a few days for the muscles to heal, as they'd spasm'd badly when I hurt myself.
But if they claim to heal all other kinds of issues, they're getting into quack territory. A pinched nerve in your spine can affect things like digestion, but I'd rather have a regular MD look at that.