Here's probably the most interesting website I found, complete with video models! http://www.public.asu.edu/~dbvan1/pr...g/boarding.htm. Their models appear to suggest that random is actually an improvement over the old back to front system, but reverse pyramid and outside-in are still better.
Here's a breakdown of the types out there and who uses them...
1. Back-to-front- AC, Alaska, AA, BA, CO, F9, YX, Spirit, Virgin, US (some)
2. Rotating-zone- FL
3. Random (assigned seats)- B6 and NWA
4. Block- DL
5. Reverse-pyramid- US (some)
6. Outside-in- UA
7. Random (unassigned seats)- Ryanair and Easyjet (2 doors), SW (1 door)

Another interesting article concludes "Among row-dependent policies which do not severely constrain passengers, random boarding (no policy) is almost optimal," Bachmat and his colleagues report. For random boarding, boarding time is roughly proportional to the square root of the number of passengers.
Nonetheless, it is possible to improve on random seating or any row-dependent system by allowing window-seat passengers to board first, they conclude." (http://www.sciencenews.org/articles/...2/mathtrek.asp)


Here's some more research...
The problem with the research is that the computer models are only so effective at predicting actual human behavior. Here is one research model, which doesn't entirely come to a conclusion, but definately interesting to read (http://www.cs.bgu.ac.il/~ebachmat/managesubmit.pdf) and a related comment (http://www.maa.org/devlin/devlin_05_06.html). A more recent article (http://www.math.duke.edu/news/awards/MCM2007lmw.pdf) recommends:
"we recommend a hybrid boarding process; a combination of window to aisle and alternate halfrows. This technique is a three-zone process, like window to aisle, but it allows family units to board first, simultaneously with window seat passengers."

They acknowledge, as I'm sure NWA did as well, that mass general boarding is efficient for SW. The major difference of course is the drive on SW to get on and get a good seat quickly (similarly to Ryanair, but they also use 2 doors). The 757, especially the 753 is a big difference of course too.

Having done general boarding on the a330, the 2 aisles and door 2L made it better I'm sure, but it still was pretty slow (especially since we were in first, and had missed 1st class boarding, and HNL has no room for a red carpet...).

As you can see, the evidence is a little all over the place...

Anecdotaly, my experience with full FL 717s is that it was slower using rotating zone than NWA's chaos on an A320.