I had been at 6, 7, 10-12 and 23 in Google's SERP's for various related search terms. Then in one night I had gotten an unprecedented 140+ unique visitors (Awstats) to the site and none seemed to be links from Google or even from backlinks. (Ok, so it seemed i'm not entirely sure that my checking methods are accurate). After the large increase in what I am only going to call traffic for now, My results in Google were gone. All I could find (with some difficulty) was a previously unknown result (page) at position 231 in the search engine.
I have the site listed with webmaster tools and I assumed I'd receive a e-mail or webmaster tools message informing me of any penalty for my site. I don't know how that even works since I've never (to my knowledge) gotten a penalty. I aslo noticed that the number of reported links to my site in Webmaster Tools increased from 2 pages linked from 8 domains with 14 total backlinks to 4 pages linked from 31 domains with 40 total backlinks. That should be a good thing right?
I also examined the meta tags and found nothing that should implicitly tell Google to not index my site. I do have rel=nofollow on some of my links in page but that shouldn't matter. I haven't made any changes to the site itself since it was "doing well" that should indicate such a drop. However, I did not that a number of individual pages have two, often exactly the same, META DESCRIPTION and META KEYWORD tags. I am wondering what if any impact that may have.