North Sails Mike Ingram has a great selection on YouTube videos that discuss sailboat tuning and sail trim.  Much of the presentation is based on J/24s.  The links are:

Tuning Beyond the Guide

• 1 – Looking at Sails            http://www.youtube.com/watch?v=BZpPZ5_vIr4
• 2 – Apparent Wind              http://www.youtube.com/watch?v=DePU8YlFj4A
• 3 – Symmetry and Balance http://www.youtube.com/watch?v=iFfymDrivSY
• 4 – Luff Curve                     http://www.youtube.com/watch?v=5tqmQMhxpe0
• 5 – Jib Hollow                     http://www.youtube.com/watch?v=vLgQdMtlJOw
• 6 – Side Bend                     http://www.youtube.com/watch?v=Hh8PC3SKo5Y