Guess it's always worth the extra 20 bucks to register the rest of the TLDs so clients won't be as confused .
I personally registered both .com and .net, but not .org as I thought it wasn't really necessary, but I know other companies registered the .org domain as well.
But usually clients that get lost would probably go Google up your company name, in which you better hope they don't use the same company name as you and get a higher rank in Google!