As of a couple days ago, CO.com is doing an impression of Hilton.com and requiring me to sign into my OnePass account every second or third page. Today when booking a flight got all the way to the seat selection screen and realized I wasn't logged in -- tried to from there and it wouldn't "take."

Had to back all the way out to the main page, login again, and then book the flights.

Kind of a pain in the (but still better than hilton.com)