I have done this before, to maintain and improve the ranking get a few backlinks that match the phrase you have already now on Google. I have launched about 15 websites this way and keep good rankings. Google sees the initial feedback from the social sites, lists your site, but it will keep falling if you don't get some matching backlinks pronto. If you type into Google cheap social marketing I have the first site, I used these techniques to get listed and rank the site. However, what I am offering is overly complex and I don't believe people understand the value of knowing Google's trigger points, when they notice the social attention, when other sites start taking the twitter/etc posts and adding them to "social conversation" websites, etc. All of this feeds back into your organic ranking as long as it is relevant.