For years, the deadline has been 2/28 to file W-2s. In a seminar last week on tax changes, the presenter made a point that this had been changed to 1/31. IRS made the change to combat the rash of identity theft (IRS will have W-2 and 1099 information to match to).
Here are the SSA and IRS links:
Also note that the penalties for non-filing of information returns (in particular intentional disregard) have increased substantially: