@InPage You nailed it! Thanks a lot. You took the words right out of my mouth as I was about to write the very same thing. ;)

Locking a site from unauthenticated users is a good feature (thumbs-up) as it encourages them to sign-up or login while they can still have a site overview through navigation menu items (Discussions, Groups, Events etc). Some people will not sign up if they can just browse the site as a vistor.

On the other hand, locking it from search engine bots/spyders is a bad SEO practice (thumbs-down). New sites rely a lot on organic search traffic, specially those with no or limited SEO budget.

UNA should be able to lock the site from unauthenticated users while allowing search engine bots to crawl its content.

Using a pop-up/iframe signup/login window over the content as mentioned above by InPage, will do. Many sites do it and they perfom well on organic search engine results.