It's kind of an insidious word -- especially in relation to the arts, where overreaching oneself is often necessary toward making truly interesting work. I've stopped using it altogether, because it's pretty much impossible to find a reliable standard on which to use it. For example: over the last couple of years I've gotten to know some New York City-based writers, and most of them had come from backgrounds unlike my own (wealthy, "intellectual class," etc). I got irked by some of the ways they acted and communicated, and my first thought was "pretentious," but, then, if they grew up in environments where that sort of thing was commonplace, then they're not really pretentious at all. The word basically means that there's a disparity between what you actually are and what you present yourself to be. And, really, who's in the position to judge that sort of thing? Sometimes you "know" that someone is being pretentious, but most of the time you just think you know, and then you look like a dismissive asshole.
http://www.guardian.co.uk/stage/thea...thbeingpretent