As previously reported, webmasters with links from paid blog networks that Google recently de-indexed have been receiving letters from Google Webmaster Tools.
Google's John Mueller talked a little about such letters and the reconsideration process in a Google Groups thread that you might find interesting (Another good find from the Google Forums by Barry Schwartz).
"While we have just recently started sending out these messages, they may apply to issues that were already known (and affecting your site's standing in our search results) for a while," said Mueller. "If you receive a message like this, and you wish to resolve those issues, then I'd always submit a reconsideration request after having done so. In some cases, you may not be able to resolve all of the issues - if that's the case, then it's important to us that you document your efforts (you might even link to a Google Docs file if needed). It's important to our team that it's clear that you have taken significant effort to resolve all of the problems in that area, and that they can trust that these kinds of issues will not come back in the future."
"In situations where an algorithmic adjustment might have been made, you're still welcome to submit a reconsideration request. It doesn't cause any problems to do that, so especially if you're unsure, submitting one is a good way to be certain," he says. "Regarding the age of the unnatural links, I'd work to have them all removed, regardless of the age. For instance, in the general case where a site has been buying links for 2 years, it would be a good idea to go back that far."
He goes on to say that you should try to wait a penalty out if you're serious about your site's standing in search. "These are generally not issues that expire after a few days, they can affect your site's standing for quite some time," he says.
Google's own Chrome landing page recently had a 60-day penalty, which may have even hurt the web browser's market share.