UPDATE:

I think we're 48 hours into this (??) ... but the figures are already looking a lot better.

Visitor : Invitations Sent : New Traffic

100 : 17 : 1

But... there are a lot of new invitations that went out... so the 17 : 1 part of the ratio will definitely decrease.

The main point though is, and always has been, the Raw Visitor : New Traffic ratio...

We went from 170 : 1 to now 100 : 1

I found one setup error that definitely cost some visits... when the script couldn't find a name, it was inserting the user's email address so the invitations were going out with hey youremail@address.com, type formatting. Also I set to include the "unsubscribe" option for these (which does cost me some visitors but helps to make sure that anyone who doesn't want to be hit with a promo 20 times can just unsubscribe). But I moved that down a little further to still leave them an option, but to avoid making the email look too much like a commercial mailing.

The actual invitation pages could use the screenshots or other mini tutorials that I mentioned which would certainly increase the # of raw visitors who use the form in the first place.

Overall, my hypothesis is that with proper setup, I could reach a 10 : 1 ratio of raw visitors to new (free!) visitors. And that's huge in itself.

Assuming just a 2% conversion on a $97 product... if your page got 10,000 raw visitors... that's 1000 new visitors which (based on this hypothetical conversion) would be 20 new sales at $97 each = $1940 just for having a viral invitation in place.

Sure those numbers are made up, but with a proper buzz campaign 10,000 visitors AND 2% conversion are both modest figures. Point is, the tool seems to be delivering value right now.