Caliban and Jhyrryl: Thanks for the great diagrams!
It occurs to me that I may be mistaken about a Lightning Bolt "line" being 10' wide, even though it affects a coulmun 2 squares wide. At 5' wide, if you cast it down a square-side, it fills up half of each "touched" square, affecting both (and providing conceptual justifiaction for "Reflex save for half damage). But you *can* cast it (using the PHB corner-to-corner rules) so it only affects a 5'-wide line, if you choose; if the Bolt was really 10' wide, you couldn't do that, and you could argue that you could have it affect a line *3* squares wide (all of 1, half each of the other two), which you can't.