We never paint anything - a wall, a piece of furniture, and certainly not a house, without swatching first. Not only do paint colors usually look different on the wall than they do in a paint deck, but we've found that the same paint color can look incredibly different when used in various locations.
While we're big fans of the sample sized paints that many paint companies are producing now, we've found it worth the cost of buying a quart, or several quarts, to try out a color before committing.
Do you swatch before you paint? Or just pick a color and go for it?