A WebmasterWorld thread reports from dozens of Webmasters that GoogleBot, Google's web crawler has not been crawling as many documents as they have in the past. Many webmasters are noticing reduction in crawl rates as much as 90-percent, relative to historical numbers.
I am not sure how wide spread the issue is, or if it is an issue at all. It might be just more efficient crawling or it may be something else.
But this can cause a lot of concern for SEOs and webmasters. Here are some quotes on that concern:
Almost had heart attack when I saw the graph drop off to nothing.
Those three days starting 4/22 had me tearing my hair out.
Again, I don't know yet if it was a Google issue or just new behavior that should be expected from GoogleBot. Maybe a Google rep will chime in via the comments. But if you see a slow down in crawling from GoogleBot, I would not worry just yet.
Forum discussion at WebmasterWorld.