One side only, no stitches. The double sided jobs I have seen have all had problems with stretch. If taped on both sides, the repair will be stronger than the origial cloth and stretch less. This will ruin the shape over time.

If there is something major, one side and stitched. No need to take it to the sailmaker if you are going to tape it together yourself. All domestic machines are up to the job. Just make sure the kite is clean (no salt) and dry. Go over the tape with a soft rag when you have taped it and work the tape so it adheres as well as possible to the cloth.

Have a look at this frankenchute, which Urban used to good effect in this years swedish Tornado nationals.
http://www.borstahusbild.se/nordicweek/mon31/slides/MV6D9375.JPG