I think the bookmarklet is a bit high threshold for some (if not most) users. Telling them to copy+paste a website URL and enter it into a field on their control panel is not.
For SEO your site could use a little work. Perhaps a blog about pregnancy could help get your domain ranking for some niche related terms. You are probably aiming for social sharing here, and organic search might be a lesser priority. Make sharing on Facebook and Twitter a lot easier (API helps) and visible (icons help). I might not sign up, but still like or recommend your app.
Also adding just that extra page to convince users to sign up, or a even demo video, can help with user engagement.
Finally I'd have a small look at making your site canonical, by rewrite or specifying canonical: http://googlewebmastercentral.blogspot.com/2009/02/specify-y... because /about and /about/ return the same content. And to quote W3C "Always declare the encoding of your document" (declare a meta charset like ISO or UTF-8 in your header http://code.google.com/p/doctype/wiki/ArticleUtf7).