As an amateur I've done several panoramas of landscapes and city views. I've mostly done it hand-held with a DSLR, with exposure lock and at the wide end of my zoom-lens. I do the stitching in Photoshop CS5 with the built-in panorama plugin. Given enough overlap I get good results with no weird seams.
What is it that a panoramic head and tripod add to the result? I know what it does and how it works (more or less), but I'm interested in how a series taken hand-held would improve when a tripod and panoramic head is used.