I debated 4 or 5 stars-- it's not as good as Frankie Landau-Banks, but it still basically took me apart. I mean I read it while I was stuck in an airport on my birthday, so emotions were pretty close to the skin, but still. Loved it. If you did drama in high school you have no business not reading this.
One thing I DO want to say though: E. Lockhart (and other YA authors) does this thing in more than one book: main character writes or records her negative feelings about a certain other person, certain other person discovers the diary/recording/whatever, casting out the main character and causing much pain and embarrassment and drama. I want YA authors to think about taking this tool out of their toolbox, because I think there should be safe space for teenagers (fictional or otherwise) to express their negative thoughts, however etched or fleeting, without fear of backlash. I mean, we all did this, and it usually turned out fine. So come on.