So you grab the .net and .org. What happens when someone buys yourname.eu or yourname.mobi or yourname.biz? How many domain names are you prepared to buy?
If someone is going to use their name, he will find a version of the domain that you haven't bought regardless of how many you have already bought.
I almost always buy the .net when I buy the .com. If I buy a domain with a weird extension, I'll also make sure I can get the .com version that includes the weird tld - Like, if I bought icey.tv, I'd also buy iceytv.com.
A domain costs what, $8/year? WheneveR I get an idea and there's a good domain for it, I buy up as many as I can of .com, .net, .org, .mobi, .biz, .us, etc. I paid $1,400 for my last important.com .. so dropping $100 to buy up all of the related domains isn't that big of a deal. I think I maintain about 250 domain names right now, but $2,500/year isn't that much money in the end.
It's far cheaper to just buy up the available names now than to hire a lawyer later to go after someone using your name.