Farlander said:
And I've mentioned it somewhere, that light and dark is not good and evil (and power and destructivity) at their base, but selflessness and selfishness at their base

Some good points there Farlander. I agree with you re: the nature of the two sides of the force (I think I more or less said something similar in the posted link on the other thread).

you can't really say that Vader is on the Dark Side at all in RotJ

I disagree. In ESB, Vader is "evil" (i.e., acting selfishly) in that he wants to get rid of the Emperor with Luke's help and control the galaxy. Later, in ROTJ, I don't see Vader's bringing Luke to the Emperor as a sign of having given up on this goal... Vader is hoping the Emperor's plan works (since he failed to turn Luke on his own in ESB). If Luke does turn, Vader'll have a shot at once again recruiting him to overthrow the Emperor (again, acting selfishly and therefore dark side).

An EVIL person who is conscious that he is EVIL and does BAD things is not EVIL.

I'm kind of split on this one. On one hand, someone who is regarded as "evil" by the majority usually does not see him/herself that way. Ricardo Montalban said as much about his character, Khan, in Star Trek II. To paraphrase: "a villain does not know he is a villain. He may do villainous things, but he thinks he is justified in doing them." Applying this concept to Star Wars would mean that Vader shouldn't have acknowledged his own "evilness" (I'm thinking specifically of the line "It's too late for me, son" in response to Luke saying there's still good in Vader). On the other hand, I suppose the above example also means a person could be conscious of the fact that they're evil, but feel justified in their actions in a kind of "the ends justify the means" sort of way.

I'm kinda rushing this response, so I hope I've made at least some sense.