About six months ago, Google began sending notifications of status updates on reconsideration requests. But there are two times where Google will not send a notification. As Susan Moskwa said in the Google Webmaster Help thread:
(1) If your site is not (never was) in violation they won't email you (2) If your site is still in violation they won't email you
But recently, over the vacation, it seems like there has been a backlog at Google slowing down the review process. A WebmasterWorldhas two webmasters complaining about the slow down in these requests. Personally, I find it funny they have that much experience with this process that they know when Google is slowing down. Maybe all they do is fix sites killed by Google?
In any event, if you submit a reconsideration request to Google and you did not fix the issues with your site or if you never had issues with your site - you won't get a response.
Update: Susan commented below, she said:
This is not accurate. We send notifications in all cases after we've processed a reconsideration request. What I said was that if you don't see any significant change in your site's performance after your request has been processed, that usually indicates one of the two items above.