Looks like there is an update rolling out right now! I have seen changes in SERP's over the past few days, but today there has been major dancing with the rankings!!
Penguin? Panda? Who knows!! What has caused the drop in rankings?
Upon the websites i have checked so far, there does not seem to be any common factor. I have noticed sites that have no backlinks (apart from natural) also being dropped so it cant be bad links. The only thing that springs to mind is over optimisation of on-page SEO, i have a feeling this may be something to do with the ranking changes. This is something i shall now look into but will obviously take a little bit of work!!
Oh what fun Google is!!
You can find out more here: http://www.seroundtable.com/google-update-now-16762.html