Seldom does a movie manage to be at the same time this dark and this funny. Nearly every line of dialogue is wickedly sarcastic--as a playwright, I spent of the time during my first viewing wishing that I could write such biting dialogue.
Parker Posey is wonderful, as is Josh Hamilton as her brother-with-benefits. The mother (the actress' name escapes me right now) is also wonderful, despite her deficient screen time. Even Tori Spelling--pariah of good actors everywhere--does a great job as Hamilton's stupid/naive fiancee (a bit of helpful typecasting). In fact, only Freddy Prinze jr. really didn't do that well in this movie, but his performance was by no means bad enough to ruin it. He seemed handily the most awkward of the bunch.
At any rate, I wound up watching it again, two days after the first time, and would recommend that anyone who hasn't done so follow my lead. Not only doesn't it lose anything on second screening, but the whole thing gets better (check out the Posey/Spellling "Marty's first girlfriend" scene)...