When I was researching Feb & March travel plans, I noticed that almost all routes up/down the East Coast were dominated by US's low prices, significantly (not just $10, but more) lower than DL, AA, Spirit, Jetblue, Airtran, Continental, and most times even Southwest. Even the US Shuttle was much cheaper than AA RJ Shuttle or DL Shuttle. I really want to book on DL (where I have status) but can't justify a premium of $100 over a cheaper US Air, so I haven't booked yet!