I had done some testing, and it seems that J.A.C.K.'s UV-lock works best with triangles (was mentioned briefly in my ATC tutorial
). But ONLY if you move the vertices in a single axis, and nudge them with arrow keys. Otherwise it's gonna be a load of texture baloney.
So yeah, either skew with the select tool, or nudge vertices carefully if you're using triangles.
ToTac has got some really neat guides that rely on the UV lock, actually. The thing is, the texture scale gets messed up, but the projection angles are right! This needs some more studying and documentation.
Also, do NOT use the clipping tool while the UV lock is on. It's gonna screw up the textures because it doesn't know how to project them.