"Previous studies have shown that a number of factors affect [dribbling], such as the radius of curvature of the teapot lip, the speed of the flow and the "wettability" of the teapot material. But a full understanding of what's going on has so far eluded scientists..."
Now scientists at the University of Lyon have identified a "hydro-capillary" effect that can be overcome either by thinning the edge of the spout, or by applying superhydrophobic materials to the lip. Superhydrophobicity is sometimes referred to as the "Lotus effect," because the leaves of the lotus and certain other plants (and the wings of some insects) are among the most water-repellant surfaces known to science.
Further details about the "Teapot effect" are available at M.I.T.'s Technology Review, via the New Shelton wet/dry.