I found a site some time ago that had a large scale (more then 3k people) internet survey, and this is roughly what they found:
Length, ave 5.5, ave variance (most of the non-5.5's fall within
1.5 inches (so 4-7 inches)
Girth, ave 5.1, ave variance .6
This data is from an internet poll, like i said, so some of it is going to be funkyness, though the variance numbers help combat that.
The girth is the part that usually screws me up, i see 5 inches and think huge, but thats really only like 1.7 through the middle.
I personaly am on the long side, and way over the normal variance on girth, which causes way more problems then it's worth (which isn't that much, really, from people i've talked to, averidge really is best).
--Bobnova