We drove to Southampton and used http://www.candps.com/ for car parking and we'd definitely use them again. Simply drive up to the terminal and they valet park the car for you, it's quick, easy and not expensive. The car was parked opposite the ship for collection when we disembarked.
First time on Princess. Check in was fine, boarding was quick and efficient, a good first impression. As the cruise was only 3 nights we didn't bother dropping our luggage and instead walked on with it. We boarded shortly before 12.30 and were delighted to find our room was ready.
Another first for us was that we had an inside stateroom and we did wonder how we'd get on but we were more than happy, the stateroom was well designed, plenty big enough and more than comfortable, and lovely and quiet. We were on Caribe deck. We had 2 inside staterooms as we were travelling with my teen son and his friend.