I think it will get to a gravity of 590 then start coming down again. Chris has just posted sales figures on his blog here: http://www.thelazymarketer.com/blog/2008/11/11/the-biggest-list-building-myth-ever-powerful-example/
I think it'll drop as the lists get maxed out, but will still stay popular for many months It's a genuine product in a fairly stable market.
The only "make money online", which has stayed on top for quite long time (and still is) is Six Figure Yearly....Others die pretty quickly.
Every make money online guide publisher should make a point of publishing the refunds too. Then only it will be treated as legitimate ...otherwise it can be a FAKE one.