UPDATE (9/23/12, 1:33PM EDT): For real this time, This popped up on Flightaware not too long ago: http://flightaware.com/live/flight/UAL7708 this suggests that United took delivery but it's interesting to note that this is a test flight to Grant Co. where Boeing conducts a lot of test flights.
UPDATE (9/22/12, 12:55PM EDT): Now getting word that it's still in Seattle. Trying to get a confirmation on departure.
UPDATE (9/22/12, 9:55AM EDT): Several sources are saying that ZA288 (LN 53, N20904) delivered yesterday, went to Boeign Field and this morning is flyingto Houston as UA 6864. It doesn't show up on Flightaware. Delivery ceremony might be taking place in Houston.
Right now a rumor but the first 787 for United is rumored to be ready for delivery and could be delivered anytime between now and the end of this weekend. Noting solid yet but I'm watching Flightaware for movement. Earlier today United's pilots took ZA288 (LN 53, N20904) for a spin around Washington State. The aircraft is rumored to be ready for delivery and may go to Boeing Field either before or for the delivery ceremony.