Originally Posted by adamqd
Good points... Also, Obi-wan is the first "known" Jedi to to retain his form and consciousness after death, Qui-gon didn't fully realize this skill in time for his own death. I think Qui-gon was more of a whisper in the force, a bit like accessing a Holocron, where as Obi-wan was almost corporeal, not so distant from life...
I remember reading up on Aayla Secura and am certain that she and other Jedi (Mace, Shaak Ti, ect) appear as Force Ghosts. She also appeared to a doctor who was a really big fan of hers, though in this case it was a trick and not the real deal.