At the risk of sounding like a marketing lecture...tag lines (and the messaging platforms they represent) only work when they are credible and uniquely associated to the company using the tag line. IMHO, "fly the friendly skies" is neither. I would also guess that a UA tagline is not aimed at the typical FT traveler, so it's not surprising that "it's time to fly" doesn't resonate well with this crowd (me included).

Great taglines are few and far between.