Image: RP_23 shock
As for Rear Shocks, Fox had a huge breakthrough with their RP23 Boost Valve Technology.
I had a chance to ride this shock for two days while at the camp and can tell you that the biggest difference was in small bump compliance. Now, it seems that the gap in performance between coil and air shocks is beginning to close. Here is what I found:
DHX RC4 AND DHX RC2