Meh, I'm leveling as Immortal with my Sith Jugg and have no problems whatsoever with either my damage or my questing speed. Rolling with Quinn I can pretty much chain pull one pack of mobs after another with little to no downtime. So while I might not do as much damage as a dps spec I don't have to stop and channel hatred after every pull while it really doesn't take me much longer to down enemies compared to others I have seen questing in my area.
And, since I'm spending all of my time in a tank spec, I'm actually, you know, learning the mechanics, abilites and limitations of a tanking Juggernaut, which in turn makes me a better tank than someone who only respecs for FPs and spends all their time not tanking.