Lift Off has two ways of sharing your site...
Sharing a live site creates a live, secure connection between your Mac and the VirtualHostX cloud servers. It then gives you a temporary URL you can give to people to view your site. When they use that URL, their request is routed through our servers and down to your Mac. The Apache server on your Mac serves up the request. This means you're free to use PHP and MySQL, etc. to build your site. The downside is that the connection to your Mac is temporary. It only lasts as long as VirtualHostX remains open. Also, some routers and internet providers can close the connection if there's not much traffic. You can always re-share using a new connection.
Technical Details: For the curious geeks in the audience, Lift Off establishes a reverse SSH tunnel from our proxy servers to the local Apache server on your Mac. We then assign you a random http://vhx.me short URL that dynamically routes your users through our servers back to your Mac. There's no reason a smart geek like you couldn't setup this sort of thing on your own, but we hope you'll like that we've already done the hard work to make it one-click simple :-)
When you publish a static site, you have the option of picking your own URL to share. Or, you can leave the URL blank and just click "Publish". VirtualHostX will automatically pick a random URL for you.