I, too, was always of the mind that Ben was his real name, and Obi-Wan was some Jedi name. I mean, that's how he's credited in the movies and action figures: as Ben "Obi-Wan" Kenobi, with "Obi-Wan" being in quotations. As another person who is not known by his real name but by a nickname, I know that you put your nickname in quotations when writing out your full name. That was always a big letdown to me when I saw The Phantom Menace.

But Scruffy brings up a good point I never thought of before. I guess it is a good thing that Luke had never been able to apply to the Imperial Academy. Geez, did Owen and Beru ever think about that? But I really think that Palpatine would have been familiar with the name Skywalker, and since Anakin changed it to Darth Vader immediately after joining Palpatine, it's no stretch to think that the name wasn't too well known. And I doubt the Emperor does his own hiring, so Luke could become some petty officer and never be found out for being Darth Vader's son.