Not that there is anything wrong with PN sailing. I prefer that at the club level, since it gets more people on the water (we race with monos, too). I agree with most that the PN numbers will never be perfect, but it's the best compromise out there.

When regattas get bigger, I like the OD aspect because I LEARN more from other sailors. There are no "your PN number is off", or "your design is better in these conditions" excuses. If you blow it, it's your fault. There are no major differences between the boats (at least not legally).

The PN racing involves more than just your routing (left/right/middle) and boat-boat tactics. It also involves TOC (time on course), which can benefit or hinder your strategy, depending on how "accurate" your PN / mods number is. I know of some people that "play the mods",( i.e, they drop their spin off the boat if they feel it wouldn't benefit them on a distance race that is primarily jib-reaching, using a huge jib in light air races) to get the PN, hoping to make it easier to win on corrected time. Again, it gets way into math, and I'm out to sail, not calculate!

To sum up, if you want to learn how to sail YOUR boat faster and improve your handling/tactical skills, you'll benefit most from OD, IMHO.