doubleofive said:

According to the PT, no one know how to make themselves a Force Ghost until Qui-Gon figured it out after he died (?!), and he taught Yoda who taught Obi-Wan. Which, of course, begs the question on how Anakin himself does it.

Wow, that's really stupid.
The ghost thing has been weird since ROTJ though.
Why didn't Anakin disappear? I think it would work nicely as a confirmation that Luke did in fact save him and make more sense that he appears to Luke along with Obi-Wan and Yoda. It would also be a cool visual to see his head disappear and the suit go limp and work metaphorically as his good self goes on to the spirit world leaving his dark side behind- the suit being a manifestation of his evil.

Umm.. that got a bit.. hmm..