Well, within the Empire itself, Vader seems obviously very well known throughout the trilogy... Everyone from Admirals down to lowly ensigns seem to know not to piss him off at least.
Now, galaxy-wide, who knows, but I've always figured the Empire was pretty significant around the Galaxy, and thus I'd think Vader is a topic people bring up. I don't know that many (beyond Palps/Tarkin) know Vader is who he was though. Tarkin seems to know little of Palpatine's ultimate background even.
I like to think though, that Vader's a pretty known guy. Consider this... Lando even seems to know how to address him properly ("Lord Vader" and all that jazz), and he's just a guy running a mining town out in the galaxy. One of possibly literally millions or even billions (or more?) type places. Fett knows this title to address him by as well.
All little stuff, and drifting off topic some, but ultimately then I believe Kenobi's well aware of Vader and who he is, personally. I think Vader has a reputation he's built up. He's maybe more infamous than famous?