While I agree that you shouldn't read too much into the metrics, something like LaunchRock gives you at least a platform to start your launch from. Much easier to mail 10-10,000 people who have expressed interest, rather than start cold and try to find that 10-10,000 people.

Don't expect your pre-launch "coming soon" page to bring 1000s of customers with money in hand, but since it's a pretty damn minimal investment, you might as well set one up.