Date: 11/16/2008 2:30 pm EDT
I installed over 400 sq. ft. with lots of perimeter. I did not use anything in the gap between the floor and the walls. I believe the gap is important to allow the floor to expand and contract. Remember, your entire floor is "locked" together and it isn't necessary to use anything under the trim.
Also, where the tile meets the door and patio door, I used a flexible color-matched caulk to fill the 1/4" joint - it turned out very nice.