Date: 5/7/2008 1:13 pm EDT
Typically the baseboard is removed and reinstalled after and on top of the new tile. This procedure in itself can sometimes open a bag of worms you don't want to deal with at which time you can resort to adding quarter-round or shoe-mold.
At any rate you don't want the tile to jamb-up tight against any fixed object. A minimum spacing of 1/8" to 1/4" should be allowed between the tile and any object. That space can then be caulked to allow for the necessary expansion (and contraction).
If the base is removed or an additional molding is added no caulk would be required but the gap is still prefferable.