A weekend WebmasterWorld thread is reporting dozens and dozens of webmasters noticing a major traffic drop due to Google. Some of these webmasters reported traffic declines in the 90% range.
Many of the issues seem to be that Google has dropped hundreds or thousands of pages from these webmaster's sites. But it isn't only large sites.
The five page WebmasterWorld thread has several theories on which sites this may impact. I won't list them all, but if you were impacted, you might want to check out the thread for similarities.
Again, this issue seem to have cropped up over the weekend and many webmasters seem to have been hit. This site did not notice a 90% reduction in traffic from Google, I have not looked at my other sites yet.
Forum discussion at WebmasterWorld.
Note: Just got back online after two days. I am a bit disoriented from the amount of information we missed. So I hope you cannot see that in our posts, but if you do, please be patient with us for the next few days.