What's the number of people who trade Bitcoin?

[Elokane]

The numbers on MtGox and the entire exchange ecosystem are growing rapidly.
I'm wondering how many people are actually involved in active trade, e.g. sell or buy Bitcoin daily, weekly or monthly. How many are new users? How many are returning speculators, just trying to make a buck? What's the average trade size and what's the average fee? Is much of it just the "same" money moving back-and-forth?

I welcome all information as well as guesstimation and speculation.

[pangu]

here are a few bitcoin statistics, but not really numbers of people trading
http://www.forbes.com/sites/jonmatonis/2012/07/31/top-10-bitcoin-statistics
http://www.bitcoincharts.com
http://bitcoinwatch.com/
http://www.google.com/trends/explore#q=bitcoin&date=today%2012-m&cmpt=q