Me too, that's why I like Ripple, since it is not centralized.
Cool. Can I use Ripple without trusting any Gateways?
Sure.
Can I use it without going through Opencoin?
I guess you mean RippleLabs... yes, the client code is just hosted on ripple.com for convenience, you can run your own rippled to connect to and set up a webserver with the client locally too (it's what I do for example), I linked the repositories before. I'd recommend to use the tagged release versions and not bleeding edge code as it is under active development.