On our last two trips we have done online check-in and it was a breeze. We didn't have any specific room requests, and really just wanted a room that was ready. We arrived both times around 10-11am and both times, at POP and at POR, our rooms were ready.
On our next trip though to AKL in November of 2013 for our honeymoon, I don't think I am going to check in online. We put in a request for a room with a king size bed, and do not mind if the room is not ready when we get there.