Whether you need a tripod or not depends on a couple of factors:
- The number of "member" images you plan to use--after a certain point, if you think you might lose track, then a tripod (and possibly a panohead) are good tools to make sure you don't miss any coverage.
- If parallax becomes an obstacle to cleanly stitching. Then a tripod and panohead are vital to make sure you're rotating around the no-parallax point of the lens. This is usually only an issue if you have subjects that are near, like, say you're shooting a pano in the living room.
With far-off landscapes, I've been able to shoot a 9x3 grid of images handheld that successfully stitched into a pano.