Here's the meat of the e-mail I got from United:
As of February 4, 2008, United has a new checked baggage
policy. Non-elite Mileage Plus® members and non-members
traveling on non-refundable Economy tickets within the
United States, Canada and U.S. territories, may check one
bag for free and a second for a $25 fee. The new policy
applies to tickets purchased beginning February 4, 2008 for
travel on or after May 5, 2008.
Wow! I haven't gotten this notice from any other airlines -- is this becoming a new standard or is United hoping to lead the way on this one? I guess you can look at this is an extra benefit to being a premium member, but most will probably look at it as another reason not to fly United. I would be surprised to see Frontier, Jet Blue, or Southwest implement this policy.