I am fairly new to blender and am far from mastering it,
But I have been recently experimenting with blender to make 3d stereoscopic (with the glasses) video clips.
These clips are quite short an bare due to my inexperience but I think you could use the techniques to make one of your open movie projects in stereoscopic 3d.
This is not the kind of 3d that requires a 3d TV; all you need are the glasses.
I think it would definitely add an extra factor to these great animations.
The only problem with having a film in 3d is that the rendering time will be twice as long, as you have to render the film from 2 different camera angles.
I think it would be too late to incorporate this into Sintel, but possibly the next open movie project.
If you like I could send some sample videos of blender being used for 3d films.
I can also understand how this could not be practical with an open source film, but I am glad to have given you the thought.
it looks like some people have already mentioned this, woops.