I ran my first guardian spec game earlier today as soon as I got my fourth 800 piece. My ilvl is ~730, and my AP is only up to 13 I believe. My 1081khp in the world became 397k in the bg. I was sad it was dropped that much, but with three sprints (not including the speed pot) my flag runs are very fast which I think takes a considerable amount of risk in carrying out. My third flag run I got caught by the horde team and beat on a bit by a twink warrior (at least I believe he was, he was keeping pace with some 99 twinks on our side damage wise, and it seemed like everyone was having issues killing him), with healing and the druid's various damage reductions I was fine. Added bonus, during a hold that went all the way to 15 stacks they dropped my healer and I just battle rezzed them back up (a nice advantage over the pally which was the other I was considering).
I'm waiting on it to be transferred to KM to be with my twink guild right now, will throw up some more updates once I see more advantages/disadvantages on it.