ZydoSEO - 4:14 am on Feb 20, 2013 (gmt 0)
I agree 4serendipity that it is important to date and log all major changes to your site. It's great when others might ask later what was going on with the site at a particular time.
If you're using Google Analytics, you can make notations in the GA timeline so you can maintain a history of all major changes to the site right there within GA. I also use those notations to log major Google changes as well when I can correlate them to a drop in rankings/traffic.