doesn't seem to work. I still have one domain that is not pointing at anything at the moment but is registered with godaddy (will move it soon!) and byedaddy says it "doesn't appear registered with GoDaddy"?
Same with one of mine. I'm wondering whether the site is merely checking to see if the domain is using godaddy's name servers (mine don't) rather than lookup and parse the Whois info (the only way to really tell).