Optimal boarding method for airline passengers (arXiv:0802.0733), by Jason Steffen. Via Cosmic Variance. Apparently Steffen is a physicist who was sufficiently annoyed while boarding airplanes to start thinking there has to be a better way.
The conventional method (boarding from back to front), although it looks efficient from the point of view of someone in the airport, is quite bad; Steffen describes it as the second worst method, after the obviously bad front-to-back boarding If you stop to think about it you realize that the real sticking point is not getting onto the plane, but loading luggage into the overhead compartment. So the trick is something to parallelize by, say, boarding all window seats first, then all middle seats, then all aisle seats. Heuristically, you'd expect a speedup factor on the order of the number of people sharing each overhead compartment. This isn't exactly Steffen's method -- his simulations show that it's best to divide the people on the plane into four groups, which correspond to people in even- or odd-numbered rows on the left and right sides, and board each group in turn -- but his simulations as far as I can tell treat the entire plane as one long row. Still, either of these makes you realize that there's work to be done.)
Plus, if you board people so that the people loading their luggage at the same time aren't on top of each other, then you get less people hitting each other with their bags. Everybody wins! Except perhaps the people in the aisle seat, in my scheme -- since they get to load their bags last, and people try to get some pretty big carry-ons on planes these days, there might not be room in the overhead compartment for them. But that's got to happen to somebody.