Start it on every character (19 times).

Progressed it on at least half.

Finished it on 1.

I got bored with it the other times. Same reason I've only don the DB quest line twice now. Thieves Guild too. Hell, only quest line I've done multiple times is the Civil War.

Completed it once and started it many times but didn't feel obliged to finish it. I played the Oblivion MQ several times and loved it each time, it just didn't feel the same for the Skyrim MQ.

I've played it through once, but started it multiple times. Definitely going to play it through again.

I'm at around 6 times which is double the amount of Oblivion. Dragonborn IMHO, adds a lot more to the main quest and makes it worth doing if you like Dragons. I think that's the key part if you can stand Dragons. I don't mind them although they do get old after awhile.