Hmm. I can see the advantage in constraining to screen plane, but I wouldn't use it much myself if I had it. Would take too much effort to LINE UP the camera exactly in the plane I'd want to work in. I'd prefer to align the working plane to a selection (which is already provided). That said, the way the views project through the planes in the assembly room makes for easier aligning. I'd like to see that same ghosting appear in the vertex modeller as well. (And please re-design the metaballs modeller to look like the other modellers!)