I saw I Love You, Man last night and must say it was a pleasant walk in the park. The movie started kind of slow until Jason Segal's character makes a classic toast at Paul Rudd's engagement party. After that, the movies picks up a bit, and all-in-all, was pretty good and funny the whole way through. There are funny moments, but other than the toast, no lines I am going to be quoting from years down the road. There is good chemistry between the actors, but several funny actors are under used, such as Andy Samburg, far and away the best member of SNL currently, and Jane Curtin.
Ultimately, definitely worth viewing as a rental or matinee. Just do not expect Role Models funny.