Anyway, from watching the real ESB, you could infer a few things. I don't know, it's a little bit ambiguous. You could be certain that Vader was searching for Luke. I mean, you can't get any more clear than "obsessed with finding young Skywalker." It could possibly be inferred to be a revenge thing for the Death Star. Or it could also be the father/son connection. Or both. Meanwhile, Vader could (and almost assuredly does) have his own motivations for trying to recruit Luke and possibly use him to overthrow the Emperor. After much thinking, here is what I believe to be the meaning behind the conversation between Vader and the Emperor. Assuming, as I would, that the Emperor always knew about Luke since the Battle of Yavin, he was sorely pissed at him for making a fool of the Empire. It's only now, though, that he senses that Luke could be a possible threat to everything, maybe because of his training with Yoda. So the message is to let him know how big a threat this could possibly be and, depending on Vader's officially stated intent, to either hurry up and get Luke and kill him or to possibly abandon his attempt to capture him alive. But Vader bargains, reminding his master of what a great commodity a new Sith would be when Force-trained people are a rarity. And, if that didn't work, he promised to kill him. Of course, he didn't mean it. Even Shadows of the Empire states that.
But the new version utterly destroys that line of thinking. Besides the previously mentioned chain of command where Vader could definitely not get away with using the fleet to search for Luke without being found out. I mean, geez, he couldn't have been more transparent if he put up a mission objective billboard. "I'm sure Skywalker is with them." And yet we're supposed to believe that three years after the fact, they're just getting reconnaissance that "the young rebel who destroyed the Death Star is the offspring of Anakin Skywalker"? That can't be right. All Vader had previously been able to pick up from being close to Luke was that the Force was strong with him. He hadn't been as close to him at all since then. So obviously Vader didn't simply sense that the pilot was his son (and magically divine his given name as well), but it was information that they had intercepted at one point prior to this frantic search. "What?! His name is Luke Skywalker? Force trained? Tagging along with Obi-Wan?" So to make it seem like they just now figured it out makes absolutely no sense, even if, according to George, Vader was just lying about it. I've already said that the way it exists in canon, there's no way that Vader could have simply sensed the information through the Force, and, had he done so, I'm sure there would have been a lot of questions about where this information came from, which would undoubtedly get back to the Emperor. So, similarly, had Vader managed to find this information through "normal" means... once again, he couldn't have just hidden it. And he didn't just hide it.
I'm sorry. This is getting pretty lengthy. I'm getting tired, so maybe I'm rambling. I'm done now.