I have a few holiday sites in my mix of sites. One in particular has been doing well lately due to the season. I haven't touched this site in almost a year, but decided that maybe I should promote it a little bit. This site runs on a particular piece of CMS software (reputable) and that software has it's own .org domain. On their main site they have a "powered by" page where users of their software can submit their story and it may or may not get posted, this is a pagerank 7 page. So, I submit a little blurb about my site using their software because it is easy and flexible, etc...you know, PR web type stuff. The next day they have my post of their pagerank 7 page, you can imagine my excitement The day after that, I notice that this page gets picked up by a lot of other sites (maybe by RSS feed, who knows), even more links, good stuff. Two days later my traffic from google drops to 0. Oh yeah, the super-geniuses at google and their fancy algorithm have dumped me for...one posting. Oh, I know that their algorithm sees it as a big rise in pagerank over a short period, or too many links too fast or some other black-hat-esque technique, but this is nothing more than having a story that people liked and picked up. I'm just about ready to give up on this stuff. I can only hope that this "mistake" self corrects soon, after all for a seasonal site like mine, the months of November and December are what it's all about. Google now has me at the point of being scared to do anything? I feel like I might offend the google gods with anything I do.
I wouldn't worry too much it should come back again... This happens a lot with one of my sites... I learned you have to change the link text around more often, another reason you get dropped from the serps.
I have also seen that with a few of my sites but they always come back in a few days. I especially have noticed it with a few of my Squidoo lenses- they go up and down constantly. Check in a few days and you will probably see it back up again.
Checking this morning (just now) I'm moving back in. Now ranked between 30-40 on my sites title. Of course two days ago I was in the top 10, but yesterday nowhere to be found (went to about 150).
Google Webmaster Tools - I'm pretty sure you can contact them if you feel your site was unfairly penalised, give it a go if needs be.