georgec said:

Owen and Beru definitely knew.

"He has too much of his father in him."

"That's what I'm afraid of."

I always figured that Obi-Wan kept up with news around the galaxy by visiting Mos Eisley or talking to other people. It probably didn't take him long to figure out Anakin was Vader. Plus, I remember in ROTS that Obi-Wan watches a video of Palpatine calling him "Lord Vader."

No, not definitely. I doubt they knew that Anakin was Darth Vader as Obi-wan would have had no way of that Anakin was still alive and would likely not have gone into too great detail.

I kind of thought that when they said the whole to much like his father thing that they were referring Anakin being a space adventurer rather than a homely farmer like Lars.

Now, if you are disregarding the continuity of the prequels, then Beru and Lars lines still wouldn't apply to them knowing that Anakin was Vader because, as Anchorhead said, the concept of Vader being Luke's father hadn't been created yet.