A few weeks ago, on an old site of mine, I had a big drop in my serps for almost ALL my keywords on the same day. It went from Page 1 or 2 down to about page 4 or 5. I started looking at pages that were linking to site, and on Google one site was showing that it may be hacked. When you visit the site (wordpress btw) everything is fine, but on the google results it shows a meta tag and meta description completely different from what you see when you load the site. I used Google's safe browsing diagnostic tool, and incidentally the site was last crawled on the same day my keywords dropped drastically. I want to connect the dots here and say that is this site is reason why my rankings dropped, but I wanted some input from others. Maybe you've had the same experience?