You can already share pictures, and music to your set top box from your PC. I assume it will only be a matter of time before you can stream video. 

I have heard rumors of a product that will let you buy digital movies through your set-top-box and it stores them on the servers and is attached to your account. You would then be able to download that same movie to your PC, Ipod, and etc. Note this is only a rumor but it would be awesome if they release something like this by year end.