Mind boggling how many updates we have had this year. They seem to come almost weekly.
Although they are all different, there seems one common trait - major search terms get indexed almost immediately when a new update comes out, but long tail results tend go into a confused state, only to slowly recover over about a 4 day period after the update. If I pick an update that was favorable to me, I will see an immediate increase in the quantity of google organic referrals, but, at the same time a marked decrease in conversion rate - the conversion rate then recovers to normal over 4 days.
Problem is, with weekly updates, that leaves the long tail search quality in a very poor state for about half of the time! We know that google is aware of this because they can see the performance metrics. There have been 100s of posts in this forum about low quality long tails, zombies etc. Why cant they speed up the index process so that their intended update takes effect faster? The only logical conclusion to me is that they just don't have the horsepower to do that. Why then not just delay the rollout until all of the data is crunched? Wouldn't this be better for their users?
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.