Disney transfers are very convenient. We had them on our land and sea last year. The only thing is you might have a bit of a wait at times but its really not bad. I believe it's $50 round trip per person from the airport to the port. They get your luggage for you at the airport and then you don't see it until you get to your room. There's no extra tipping, at least that I know of. You also get to watch the video on the bus and its very nice if you never been on the cruise.
If you are staying at a resort at WDW and plan on using the transfers, you might want to find out when (and if) the bus picks up at the hotel. We were at POR and it didn't arrive until 12:15pm. We didn't arrive at the port until 1:30 or so. Plus, there were alot of people from our hotel so there were 2 buses. The first one filled up only partially and then went to Animal Kingdom to pick up a group that opted to go there for the morning. We went on the 2nd that went straight to the port, but we had to wait a little for it to arrive.
This past year, we had plans to rent a car afterwards, so we used a town service on the way. I like this best if budget wise it makes sense. You schedule your pick-up times and there's no waiting for anyone else.
We plan on using a service again. We have used Tiffany Towncar twice (last year and two years ago for a WDW trip only). We had great service. For the three of us, I have been quoted $150-$160 plus a tip. There is a bit of a difference in price, but I think it's worth it to have the availibility.
From the airport, I believe I saw that someone posted that the buses started leaving around 9:30am. I'm not sure if they leave any earlier fro the airport. I don't know how early they leave from any of the other hotels. Maybe someone else has this info. I did inquire about the times last year and I don't think it was very early for the first buses from any of the hotels, maybe around 11, I'm really not sure.
If you have a land/sea package through
DCL, you shouldn't have to go through check-in at the port. I don't think this has changed. It was very nice to walk into the terminal and right onto the ship. Of course, we arrived well after the ship had started letting cruisers on.
If you want to get to the port early from the hotel, I suggest that you take a car service.
Have fun.