So then... back to the ghost thing... (SPOILERS)
Ah, the perennial topic returns...
Not that I have actually read it myself, but I have been told that both the AOTC novel and the 'Art of AOTC' book make strong reference to Qui-Gon trying to communicate to Anakin just before he wipes out the Tuskens.
And more to the point, Yoda ALSO hears Qui-Gon, as he is probing the Force to try and feel the future at the time. The book (apparently) notes that this is a considerable surprise to him- for he had no idea that a Jedi could continue to do anything after death at all.
Well, we'll have to see what is included in the film itself- but damn interesting, eh?
I am sure queeq and myself can argue this one to death; I can't be arsed to re-count everything we have said on this subject so far...