I think the personal statement matters quite a bit. As others have stated, it is the only thing the differentiates you from the rest of the pack. Most schools get several thousand applications and many people with the same numbers and similar EC's.
I think it is very important to write a personal statement that paints a positive picture of you and demonstrates your readiness (intellectually and emotionally) for medical education. The personal statement is a hardcopy representative of your personality that is available to the entire admissions committee long after your interview. If you can demonstrate the same positive characteristics in your interview that you display in your personal statement, then the two or three people that interview you can tell the other thirty people on the admissions committee that you are a lot like you personal statement portrays you. I put a lot of energy into my personal statement to make sure I demonstrated good communication, maturity, integrity, etc. In my opinion, taking the PS lightly is a gamble at best.