If you can get the .com how important is it to have the .net and .org as well as domains for potential competitors and defensive domains like companynamesucks.com?
For the $10 it costs you to register another domain, I'd say it's worth the price to get the .net, .org, and possibly some European/Asian domains if you can see yourself doing business there in the future.
I wouldn't go into companynamesucks.com and the like though - there's no end to the number of such domains that people can come up with if they really want to hurt you. A better use of your time and money would be to make sure you don't give customers a reason to say you suck...
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.<p>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.