POSSIBLE SPOILER - In some way "How to Alienate Friends...." is the "loser learns to adjust, becomes successful and finds out that something else matter more" type of story, situated in the celebrity business. - END OF SPOILER
I don't know the original book but this comedy delivers several good moments. Though I do think the ending is flawed. It felt too fast and too abrupt, as if something was missing. Besides I'd say the movie isn't able to keep a high level. Apart from this you'll find a sweet selection of actors and actresses with sometimes controversial acting qualities. Until now I've never seen Pegg any different. Still he is a very unique type though on the screen he sometimes might seem a little more tedious than necessary. Fox proved she is capable to play a hot starlet with her head in the clouds. Don't know whether it was a hard thing to do, but her performance was hot and way better than during "Transformers" (okay... probably that's no tough match). Kirsten Dunst is very much Kirsten Dunst (again) and you may like it (as I do) or find it annoying. On the other hand you'll see Anderson who proved her acting skills and Jeff Bridges (who is fine but perhaps he could have acted a little more powerful). They all fit their character well enough.
Conclusion: I think it's a nice celeb comedy with some more and some less funny passages, a sweet cast but an all too sudden ending.