The importance of the PS is hotly debated around here. According to non-SDN "experts" that I have spoken to (professors, health professions advisors, etc) the PS is a relatively unimportant part of your application. ADCOM members probably spend only five minutes reading it, if they read it at all. Maybe they read it right before they interview you to get some idea of who they will be talking to. I am sure that others will jump in and say how wrong I am about that, but, like anything else in this process, I'm sure it depends upon not only the school, but also the individual ADCOM member(s).
My philosophy: I'm sure a bad PS can hurt your [otherwise good] application, and I'm sure that an excellent PS can help your [otherwise bad] application. While, like everything else, I am striving for excellence, I'm not trying to be too cute, so that, in the end, I will probably have a solid PS that may not be as flowery and ornate (telling stories about helping poor people in Africa, etc) as those of others, but answers the question(s) asked in an easy-to-read manner.
Common sense tells me that a solid and unique, but not excellent and worthy of the pulitzer prize PS will not hurt your chances for admission. I think that such a PS can be written in 2-3 hours (even though I've spent more than that on mine because I feel very constrained by the 5000 character limit and keep changing what I am including and what I am leaving out.)
