A WebmasterWorld thread has a webmaster who was kind enough and not embarrassed enough to share he let a domain name of his expire, which resulted in his site being removed from Google and then a month of really bad rankings. He shared his story so that we can learn from it.
In mid-July, a domain name of his expired and renewed it as soon as he found out. A week or so later, the site was back in but the traffic was down about 50% from Google. By August 6th, traffic was still down but only 40% at this point. Then on August 15th, about a month since the domain expired, the rankings were back to normal.
When we covered this topic back in 2009, we were told the rankings and everything came back to normal within a few days. I am surprised this took a full month, unless there are pieces of information we are missing. Such as the domain expired for a long period of time? There were site bugs, crawling errors, etc for longer periods of time?
Most webmasters and SEOs are surprised it took a full month to return back to normal here.
Forum discussion at WebmasterWorld.