I'm not convinced... if someone is too lazy to register, they won't be of much benefit to the community, I don't think. If you're not interested in building a dedicated community, you can always leave it open for anonymous questioners.
Having said that, I can see how it might be useful to let people ask a question and then tell them they can't ask it until they register. Save the question as hidden until they register and then make the question appear once they do. Something like that I think Askbot does.
BTW, I didn't vote your question down in case you were wondering... not sure who's the meanie, sometimes people just vote to test it out.