How soon in new relationship to introduce your kids?

This conversation comes up often and the feedback I get is mixed. So I figured it would be a great topic for discussion.

How soon after beginning a new relationship should you introduce your kids?

I have been a big believer in waiting until you are sure the relationship is for real. No need to bring someone into your children’s life  only to have them gone sooner or later. I have been challanged by others who say they do not even want to begin building a serious relationship until they see how they interact with their kids.

What has been your experience and thoughts on this issue?