I finally got my epic flying mount for my main the other day, and boy is that thing fast! 5200 gold well spent, if you ask me (5000 for the training, 200 for the mount itself). There aren't too many flying mounts available in game. Alliance get the choice between four different colors of gryphon: blue, red, purple, and green (I went with blue). The Horde counterpart is windriders, which come in yellow, red, purple, and green. Additionally, both factions in theory have access to the Nether Drake. Members of the top Arena team on each realm at the end of each season will get an armored Swift Nether Drake, which gives a 310% speed increase (other epic flying mounts are a 280% increase). For those of us who aren't going to be making it to the top of the Arena ladder anytime soon, Blizzard have said that there will be a way to get a 280% (non-armored) Nether Drake via questing, which will be "difficult" but not require a raid. Drysc also said there will be a 310% speed boost counterpart to the Arena reward, though he was unable to give details on how it might be attained. I'm guessing massive gold sinks.
Have you got your epic mount yet? What color did you go for? And do you think it was worth the gold?