Just throwing in my two cents on a few of the topics discussed here.

Fett - stop the Fett fan service. He's menacing in ESB because he doesn't say much and doesn't take any crap. He even questions Vader in the carbonite chamber (ballsy, isn't he?) There's nothing wrong with him never being seen in ROTJ because he made his delivery to Jabba, collected his money, and he's off chasing down some other poor schmuck.

Force ghosts - I read all of the posts and agree with many of the attempts to explain it all. It just hit me, Obi Wan says, "You can't win, Darth. If you strike me down I will become more powerful than you can possibly imagine." He has learned a deeper connection to the Force than Anakin ever did (hence Vader's surprise). We see lots of jedi bodies in the PT because they never escalated to that level. Even those on the Jedi Council hadn't figured it out. Yoda did because Yoda's amazing. Obi-Wan figured it out through meditation and discipline in his years in hiding on Tatooine. Maybe he also took midicholrian injections [ducks and covers]. If you leave out the whole nonsense about "teaching Obi-Wan to commune with Qui-Gon's ghost" in ROTS, it's a plausible explanation. I don't think Anakin deserves a force ghost at the end of ROTJ, but it does give it a nice happy ending.