When you are trying to get into a university, a grad school, or even a specialty school, more times than not a personal statement is required. The first thing that you need to do before you begin to write your personal statement is to write down all of your thoughts. After that is done you can begin to edit your work. You may want to believe that your first thoughts are gold, but in order to write a successful personal statement you must edit it often.
If you are applying to several different schools using one generic statement will be easily recognized and just as easily dismissed. WHY _ because you will be seen as not making an effort sell yourself to this particular school, low effort equals low interest to admissions representatives. Remember the admission committee will likely view thousands of these statements from qualified candidates and they will spot a weakness, flaw or lack of attention to the process in a heartbeat. What you don't want to do is give this committee an easy excuse to dismiss your statement and application.