I definitely experienced a substantial drop (-2 to -7 slip) in my rankings. I started noticing the drop on Wednesday (April 6th) with one keyword that I track.
It blew me away when I came into the office today (April 8) and did my routine ranking check to see the rest of my keywords fell too.
I wasn't hit by the first Panda Update. In fact, I benefited from it. Something's up now, though. I know it.