anteck - 1:17 am on May 7, 2012 (gmt 0)
I was just looking over my analytic's and came to the same conclusion. Right after the april 24th update, the bounce rate on all my sites shot up, despite being fairly consistent for months.
I think it's safe to say that google throw out a lot of the 'user metric' data when they do an update.
On most of my sites the bounce rate is now slowly decreasing, it's obvious google are relearning how to rank and index things.
It's pretty sad that it's come to this - when google have such poor control over their own index that they have to launch updates which kill legitimate sites, send rubbish traffic, and constantly restart all over again.