The 2014 filing season was originally scheduled to start on January 21st. With the delay, the IRS is not going to accept or process 2013 individual tax returns until January 28th at the earliest, February 4th at the latest. Even though they moved their start date back, your deadline is still the same.
In addition to the 1 million items of correspondence the IRS was already processing when the shutdown occurred. A mere 400,000 more came in during the shutdown. That should definitely help with their efficiency!