The latest Google Webmaster Help video deals with getting your site's rankings back after experiencing some downtime.
Google's Matt Cutts will often provides answers to his own questions in these videos. This time the question comes from Googler Pierre Far, a Webmaster Trends analyst at Google UK. The question is:
My website was down for a couple of days and now has lost all of its Google rankings. What can I do to get them back?
Basically, Cutts' answer is just to put the site back up, make sure it's reliable, and make sure the pages that were there before are still there.
"There's a tension at Google where if a page goes away (maybe there's a 404), we don't know if it's really gone away or whether that page will be back," he says. "Sometimes there's a server time out, you know, the server is kind of slow. And so, on one hand, you don't want to keep showing a page that would be a bad user experience, like it's really gone away. On the other hand, it's very common for websites to go down for an hour, two hours, a day, two days...and so you also want to give the benefit of the doubt, so you can revisit those pages and see whether they've gone up."
"So we do have different varying time periods where we basically allow, if a domain looks like it's gone away, but it comes back - you know, it's back online, then we just sort of say, 'Okay, it was a transient error,' so the short and simple advice is just make sure you put the website back up the way it was, and hopefully things should recover relatively quickly," says Cutts.
This may not be quite the answer you were looking for, but that's the one Google is giving. It would certainly be interesting to know more about these "varying periods of time".