I've just completed my first-ever co-registration/lead generation signup tracking dashboard. You can find it at http://xnnd.com/cr/ and it will update daily. As time permits, I'll add additional information and detail to the dashboard.
Today, you can look at it and see the number of messages received at the handful of testing mailboxes I've used to track what mail co-registration and lead generation send to their list.
For example, if you look at my "freeipod1" signup, you can see that this mailbox has received 557 email advertisements since February 1st. If that was your personal Yahoo mailbox, would you feel overwhelmed? Would you expect that a single signup or a few buttons pushed on a "free ipod" site would generate so much mail?
Below that I provide a breakdown of the top 50 IP addresses seen in this mail stream; ranked by number of messages received by each IP address.
I created this process on February 1st, 2010. Every day or two I added another signup or two. Now I'm up to seven active signups, and those seven mailboxes have received over 2,900 messages. Average that out and it's about 414 messages per mailbox. The sending volume seems to vary across the streams, though, so some of the accounts have actually received many more messages than that. Ouch.
You can find a list of every IP address found in the mail stream, linked from the dashboard. There's also a very simple RSS feed that I created, showing the last 4 IPs to send mail into that mail stream.
If you're interested in some specific data in some format or other, feel free to drop me a line.