I think the Flash is pretty well-known all around, but yeah, I remember when the GL movie came out, a lot of people had him confused with the Green Hornet (it didn't help that GH also had a movie that year).
The thing is, I love GL (Hal, John, Kyle and everyone else) but I feel like the brand is tainted now with the GA. When I mention Green Lantern to someone who isn't a comic book fan, they tend to get this look on their face like I just farted. That's why I think that WB should hold off on GL for a while. It's a tough concept to get right on the big screen; the GL movie's failure with both critics and audiences more than proved that. WB should make the Justice League movie and figure out how to get Superman, Batman, Wonder Woman, Flash, Aquaman and Cyborg to work together (if that is indeed the roster) and THEN introduce GL in a sequel, once they've tackled the easier characters.