I thought about this exact issue before I ordered my 2012 MX RSL. I didn't get it because it was not an option, and many mfg bike reps told me it wouldn't matter on a hardtail. That said, I did get the new Rock Soc XX World Cup tapered fork with the 15mm axel. Jon's right in that parts that move will benefit more from the 142 axel. It really matters in my fork. Will 142 stiffen the frame, likely a little, is it worth waiting for, heck no! Let me explain.
One of my riding buddies best describe the bike like this. "The Moots is a mile in front of me and my lungs are a mile behind me. The thing is flat out fast!" Many of the same guys I ride with now have new carbon 29er's of different strips, and they use my RSL as the reference.
Lastly, if you get one don't skimp on the saddle post, stem or bars. I run a Moots post, stem and bars and they really affect the ride for the better. My 18" frame only weights 20.5 pounds with pedals! 3-4 pounds lighter than my buddies carbon frames.
There are a lot of bikes in the market place to choose from, most are made of carbon and glue. A MOOTS is made of Ti and solo. Each day you wait is one less you don't get to spend riding a Moots!
Good luck, and keep the rubber side down.