Don't forget Gain, Volume, Proximity/angle of guitar in realation to the speaker, the wood your guitar & fretboard are made from, whether the string goes thru the body of the guitar or is just mounted in the bridge (like a Jem). *Also, you're more likely to get better sustain on the 5th fret than you are on the 15th, simply because there's more string there to vibrate.
Sometimes if i'm going for a 'forever' note, i'll kick open my wah and put on the
bridge pickup - that helps.
Some people also have better sustain in their fingers than others - there's definitely body mechanics if you're going for natural sustain. *
Compression can only do so much and has "side-effects", such as amplifying picknoise, etc.
good luck
~K
(Edited by kennydoe at 9:22 am on Mar. 22, 2002)