[shanecleveland]

I've done this on some small sites, and it doesn't have to be a 404. Though that could work. I also do not recall the origin, but I definitely stole the idea.

I tend to use a "call to action" – "Sign Up", "Register," etc. And then link to a landing page with a "Coming soon ... " message. I have also had an option to submit an email to get updates. So I could track both hits to the page and compare to how many also submit an email.

I am not sure which is better. A 404 may detract from confidence of the site, and it may also lead to a single user refreshing the page or visiting multiple times, thereby skewing the results. Though, a landing page may also be annoying for the user.

I do think it can be done in a way that can both test actual interest without abusing the user.