Jason Segel's penis probably would not sell a lot of tickets all by itself. Not that there's anything wrong with it, but most of us don't think of the co-star of "Freaks and Geeks," "Knocked Up" and "How I Met Your Mother" in that way. As wise men (and women) always point out, it's not the thing itself that matters, it's what you do with it. And what Segel does with it as star and writer of "Forgetting Sarah Marshall" is magnificent. Between his brief nude scene at the very beginning (a humiliating, emotionally naked break-up and breakdown), and his even briefer final one (a welcome reunion of sorts), he discovers quite a lot about himself through his genitalia.