Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
My MM slow down also when my MB is doing anything intensive. First off, the mouse itself lags due to the wireless connection. But, when your machine is using a lot of resources it'll slow down even more. You could get more RAM to solve the problem or use a wired mouse. I use a wired mouse for PhotoShop since I like to have very accurate control.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.