OK, Rootman, head right on over to the confession thread (either here or the 41, for your convenience) and plea for forgiveness for starting an average speed thread. The only threads that are worse are "are bike helmets really necessary?", and "do you carry a gun when cycling?".
The most fun I've had lately on a bike is when I rode over to an area where the construction of the Louisville Loop is underway. I rode on partially completed trail, some of which was little more than beat-up doubletrack, even more fun when you try it on a SWB bent. My average speed was around 10 MPH.
Average speeds are also affected by group rides (faster if you can hang and draft), terrain, and density of traffic and stop signs, lights and the like. I don't think it's a very useful number.
And mine is always slow, anyway.
__________________
Momento mori, amor fati.