United Airlines will be charging an extra $5 for bags checked at the airport, or $20 for the first bag and $30 for the second unless you check bags on their Web site before departure. This new fee is effective May 14 for travel before June 10. If you book your ticket prior to May 14, there's no fee. And there are the usual exceptions from paying fees for high flying members of the United frequent flyer program, first and business class customers, and certain other passengers. Thus, United matches a similar fee recently announced by US Airways.