It only took about a month and change to get to 100 folks a day coming in from organic SEO, and that was when I was young and much less savvy about it. It is really, really achievable if folks are looking for what you have. All you need is solid meat-and-potatoes onpage optimization (title tags, effective keyword use, all that jazz), minimal linkbuilding (ask friends to link to you from their blogs or do Peldi's thing), and (the one I frequently find missing on new software sites) sufficient content to get search hits for. You don't want to try for SEO using the typical five-pages-with-150-words-max that most folks use as their starter site.
This is a compelling reason to put your site up prior to launching, by the way. Heck, put it up before you even have a product coded. (My next one is up already and getting a wee little trickle of traffic with just a few paragraphs and a link to a Wufoo form for folks who want to join the beta after I, you know, get around to writing it.)
Congratulations for the fantastic work you've done. You're really an inspiration to many of us. If I may ask you a question: How would you manage SEO if you were testing several product ideas at the same time and needed the 100 clicks/day for each one of them? Is content the main thing? Thanks :)
I would install Wordpress MU and make every site a blog (structurally speaking) so that the overhead of adding content didn't crush me. I'd also think about hiring freelancers to thicken the sites out with articles about the problem domain and customers.
At 100 visitors a day, yeah, content and onpage factors will largely suffice. You're going to eventually need links to build the sites up, though.
This is a compelling reason to put your site up prior to launching, by the way. Heck, put it up before you even have a product coded. (My next one is up already and getting a wee little trickle of traffic with just a few paragraphs and a link to a Wufoo form for folks who want to join the beta after I, you know, get around to writing it.)