I upgraded last year, right before the MS150. It was mainly out of necessity (my aluminum bike died). I wasn't looking for a carbon frame, but the shop had one in my size (I'm tall, 6'-3") with the components I was looking for, so I paid a little more than I was planning. Let me tell you, the lighter frame is noticeably quicker and more responsive than my Al frame. My average speeds started climbing immediately.

Another thing... I've started doing some group/shop rides. I never imagined I could go 20+ mph for any sustained distance, but if you are drafting with a group, sharing the load, working together, etc. it is amazing how fast you can go. And it's fun too.