I put worrying about this (and paying for lesser domains) in the pointless waste of time and money box. It's more important to test ideas fast and cheap than to protect a non-business from unlikely squatters. Who goes to the .org site first? No one whose business I'm worried about losing. The investment has zero return, and protects you from nothing if you have the .com. I changed names 4 times for my last idea; I'm very glad I never bought the variant domains.

Edit: On top of the reasons above--if you get to the point where you've trademarked your name and succeeded, I think you can kick people off the squatter domains through legal means.