simple once a driver is ready.
samba for windows shares and nfs for linux shares. It should also be possible to mount via UPNP if your media box supports it (djmount via fuse)
I'm not streaming a thing. I'm going to have 32GB of card space for a reason.
However, if I were to stream, I'd be using a dedicated server/client that supports remote media as a specific feature. I think MythTV was one idea, but I'm sure there's quite a few other options out there.