If you put your link to public places like hacker news, then google will find it.

If you simply create a post page and keep it to yourself or share in a closed social network (e.g., IM, facebook private group ...) that cannot be indexed by google, then you are good.

That said, you decide to what degree you want to share your page.

This is not correct. With Google now having Chrome and other tools, there are many ways for Google to find out a URL exists.

You may want to send a follow up email with a quick link for the user to add a noindex meta tag to the page, or even password protect it.

Thanks!

We just did a release to address this problem. Now, <meta name="robots" content="noindex"> is added for each single page.