Galleycat brings some attention to two very similar covers: the now quite recognizable "Prep" jacket and the cover for a new novel from St. Martin's—"Posh". The similarities were also noted by a SF Gate review of "Posh":
The novel's cover design -- with its photo of knotted, mint-green sweater sleeves and its four-letter-word title beginning with "P" -- blatantly mimics, as others have noted, that of "Prep," Curtis Sittenfeld's 2005 best-seller.
While they are quite similar, my guess is that it probably wasn't the designer's choice to replicate the feeling of "Prep". More than likely it was dictated by someone (editor, author, marketing?) trying to play it safe or follow in the wake of "Prep"'s success. Smart approach? Seth Godin says it's what's on the inside that counts.
I think it would be interesting to see the other comps presented for this title.