I'm a vote for having both domains point to the same site - as long as the .com one has a
permanent redirect. I think having two separate domains defeats the real purpose of having both domain names. I can often remember a website name but not the tld. Since it's usually a .com or a .co.uk, then if you have both I'll always end up on the right site.
If you're going for world domination then make sure you grab the .org one too - you can use that for your charitable foundation when you "retire" and will be forgiven for it not being redirected to the main site

Paul
<edit: typos, but I bet I've still missed some>