I’m thinking of registering a misspelling of a popular site’s domain name (example: Yahhoo.com, AOLL.com). Is that a good idea?

This is commonly known as “typosquatting” i.e. buying a domain name with the expectation of siphoning traffic off of the legitimate site by snaring people who can’t spell well. There have been a number of court cases as a result of this kind of behavior – most were decided in favor of the site owner. Ultimately, it’s your decision.

Thanx stevon, I’m thinking of registering the “.org” of a well-known .com domain name. Is that a good idea?

While this tactic may get you some “free” traffic, it’s also a great recipe for a lawsuit. If the .com domain is trademarked, it’s better to steer clear of trouble. If the .com domain is “generic” (that is, it is a dictionary word which is not trademarked) then you’re safer. Ultimately, it’s your decision.