And congrats on the wise decision to go with an MX500 might I add! Try removing the weight, it never bothered me, I just felt like cracking it open and trying. It's noticeably lighter now, and quicker!

Be careful not to lose the spring or the little metal clicker arm that are set up around the mousewheel though. It's pretty easy to put back together, but if you lose them your toast! (not really, you just lose the notch effect when turning the wheel or it won't be as hard to click down).