OFF THE WALL PS STUFF:
An MD/PhD I know wrote about how getting into medical school is a lot like a game of chess. But then again, he's kinda Machiavellian.
Obviously, his rather outside the box statement did not stop him from getting accepted.
But I get the feeling that for every gimmicky personal statement that works, there are about 50 that annoy the adcom to no end. So, it's a tight rope walk to try not to be *too* unique.
As others stated, it's good to have a little of everything in your PS. I found it helpful to mention specific examples in my life, and then discuss how each instance impacted my drive towards a medical degree. Being specific (but not all over the globe with your examples), helps the committee have a solid picture of you (and when you're a more salient applicant, you will get better results, in my opinion).
Medicine is a very conservative field, and this definitely includes medical admissions. Most often they want a little bit of ego-flattering (ie, no critiques, and a smattering of "I know how physicians make a positive impact" - not TOO much ass kissing, tho). They want at least one or 2 solid examples of WHY you want to do medicine (some variations: how you have tested your resolve to go into medicine, what hardships you've overcome, etc) and, most importantly, what you've learned from these examples.
HUMOR: You can use humor in a secondary way - for instance, in my PS I quoted another doctor's humor in the face of a patient's scary cancer diagnosis, and wrote about how it helped the patient and the family, as well as the doc cope with the stress of his job. You probably don't want to make *your own* jokes, but if you can think of any health-care related examples in your life that brought levity, it might be appropriate in your PS.
You also want to reveal that you KNOW what you are getting into. Medicine is tough. If you can respectfully mention a specific example of how a doctor you respected faced adversity (it doesn't have to be a trauma - I wrote about how a doc I shadowed admitted she was always a little paranoid at her job, but it also helped her not to get sued, yet. It's a real fear in medicine, now). Oh, but don't be cocky and say you know everything.
So, in conclusion: in your PS you should be specific with examples, talk about the lessons you've learned, be conservative and upbeat if you can, show you understand what you're getting into, be HUMBLE (doctor's are by and large a very egotistical and insecure lot - don't make them feel threatened...make them feel you're HONORED to have your paper looked at), be empathetic, be a little nerdy (you love science!), use humor and weird gimmicks in moderation, and BE YOURSELF.
Good luck!