In short: on 17 May I have my highest Google traffic in a long time, and a day after it's down to 30% of it's average. I checked Webmaster Tools, and I found only 1 Crawl error, dating from 17 May: http://www.mydomain.com/index.html - 404 (Not Found) But seriously, I've never had an index.html, only an index.php! Here is a screenshot of both my GA and Webmaster Tools accounts: http://img248.imageshack.us/i/screenshot4td.png/ Ps: I just redirected index.html to the root domain, to see what happens.
Maybe nobody needed to make logos those days. Google is constantly testing and changing serps and your website probably got hit with something during that time.
At least give it a couple of weeks to see if it comes back. Trying to fix it too soon could cause even more problems.
It would be an way too drastic drop just because of an algo change, IMO. Man that's hurting me bad... I really hope it comes back soon. Yes...