It's funny... I started writing a "Why Michigan" essay for my application. And in the end I had to crumble it up and toss it out. I'd love to get into Michigan. But the only honest reason I had was "it's a damn good school." While I thought my essay was passable, I just knew if I was reading my application on an adcomm, I'd think I was full of crap.
Ended up just writing two other optional essays. I'm afraid now that my reluctance to write the "Why Michigan" one will be the thing that gets me rejected, despite the fact my numbers are good for UMich. In retrospect, I probably should've just sent in the "Why Michigan" essay even without being entirely satisfied with it.