Good stuff on jumping technique... I recently put a video up, mostly summing up alot of what you all have said. Hope it can be of some additional aid.
YouTube - Gain 2 - 6 inches with better jumping form.
Overall I think is a big help.
1. Get warm - increase the elasticity of muscles and joints. Increase blood flow to muscles.
2.Stretch - further increase elasticity of muscles and supporting structures. Warm and elastic opposing muscle groups allow full contraction.
3. Eliminate mental blocks - Don't allow your mind to interfere with performance.
4. Exaggerate last step - This lowers body prepares for lift off.
5. Use whole body - Prep arms and lower back to be involved in upward explosion. Point toes toward knees to get full range of motion.
6. Successfully transfer momentum - Allow forward momemntum to be successfully transferred upward, instead of "killing" it at the point of take off.