As far as i'm concerned the longer the delay the more polished Dawnguard will be on the PC, Just as long as the wait is not as long as for half life 3.
Yes, it's been five years since episode 2 was released, and keep in mind, there was an excruciating 6 year gap between HL 1 and 2, although 2 lived up to the hype. If we don't get it next year I will be pissed.