Jessica I read About a Girl and thoroughly enjoyed it and I did not read the books that came before it. It stands on its own.
This answer contains spoilers… (view spoiler)[Good god, yes. Not because it's a linear story, but because #3 offers the only hint of redemption in the entire series... I read this one first, not realizing it was the end book. I have just finished 1 and 2, and now I'm horribly depressed... but very IMpressed as well. (hide spoiler)]