A site of mine took a huge hit yesterday (April 6) too. It had the #3 position for [best widget] at the beginning of the day. Sometime before the day was over, traffic fell off a cliff, and I discovered that that the site dropped to page 13 for [best widget].
US site; new site; launched 5 months ago; domain registered years ago. Has yo-yo'ed before, but #3 for a week was the best it's been, and I was hopeful it'd last this time. Sigh.