If you've only used the humble bundle site and not OTHER bundles, you can look at your user details and see which ones were from "CD Key" rather than "Steam Store" as a source.
In the upper right hand corner where it says (username)'s account. Click there and select account details.
On the Licenses + subscriptions page it shows "Retail" for any game not purchased on steam... on the "Store transactions" page it shows under "event" as "CD Key" or "purchase". Then again, I don't think this will help you if you've bought games via some other store like Greenmangaming.com or Amazon or whatever.
It's a start... just count up the number of games marked "CD Key" and then do some math. --- http://raptr.com/badge/arleas/uc.png http://www.speedtest.net/result/3635582762.png