Next to Dune I think that Blue Velvet has to be one of David Lynch's most linear movies with definite plot points that intersect with bizarre but somehow touching moments. I agree that David Lynch isn't being preachy, in fact I would venture to say that he is fairly similair to Nabokov in his ideals of simply recording what he deems beautiful or interesting to him. There is no character that I can think of, with the exception of Professor Hess in The American Astronaut (http://www.youtube.com/watch?v=MkBYGXL63PM&feature=related) , who is as batshit crazy (and thus interesting) than Frank Booth. The devil is always more interesting than God. You can always predict what God is going to do, the devil is a bit more complicated. I mean if you believe in the Christian story then the devil knows he's going to be cast into the fiery pit, but he keeps on tempting and seducing.
My favorite scene in Blue Velvet merely because of its complete absurdity is when Frank applies lipstick (badly) and says "pretty pretty pretty" and kisses Jeffrey then asks if he's ever gotten a love letter..."it's a bullet from a fucking gun..fucker. If you ever get a love letter from me you're fucked forever fucker.". Also there is the priceless line to use at parties "Heineken! Fuck that shit! Pabst Blue Ribbon!" It's only amusing until someone looks at you like you're the biggest asshole that ever trod through the threshold of their door and even then it's still pretty funny. I'm sure David Lynch would be proud.