I know I would generally use the same essay, but with current information integrated in. I saw an essay by a reapplicant (who got in the 2nd time), and he actually acknowledged his previous application and how he improved his application that year. For me, much of my historical information that I included in my essay obviously won't change, so I still would want to include that. But I like the idea of acknowledging my previous application and updating/including new information that shows you continue to love medicine and are motivated to get into med school.
I changed mine in its entirety. My first PS was about my life as a whole, sort of step by step showing how I arrived to where I am today. Decided to scrap that and make it more focused. I decided to amplify my discussion of my childhood (parents are physicians) and of my community service. Other facets of my life I still mentioned but kept concise. At any rate, I think Kenon's suggestion is just as appropriate, but I would definately NOT use the EXACT same PS.
I didn't use the same statement and I don't think you should. The way I think about it, if they didn't like my PS the first time around, they won't like it the second time either! You gotta present them with a new application.
I did what Khenon suggested. I kept most of the background info, but said that I was re-applying and explained why I thought I was a better applicant this time. Basically, I kept the first half and changed the second half.
I actually spoke to some admissions people about this question when I realized I had to re-apply. They said you should definetely at least tweakit to show what has changed in the past year. One of them said "if you don't (change it) it looks as though you are lazy and that is the last thing you want admissions committees to think." I personally rewrote mine including the most vital aspects of my previous PS and focussing on my activities since. I figured (and found out by asking the admissions offices of ten schools) that the ADCOM have access to your previous application if you applied there last year so you want to use the ne PS as a way to convey more about yourself that will add to your previous PS and application as a whole. Good luck everyone.