I'll have to beg Brett's forgiveness for dredging up the past but WebmasterWorld is actually one of the few cases where this very issue has been discussed and resolved with Google's Matt Cutts on his blog.
Matt said it was cloaking when WebmasterWorld originally put up a login page first, before showing any content. However, after Brett changed the code to show one page, the page Google indexed, and then show a login page if you tried to go further, it was no longer considered cloaking and resolved.
So based on that thread from Matt, what you're describing with facebook is definitely cloaking and against Google's rules unless they show you the exact page Google indexed before requiring a login. If you've already seen one page from a Google search and then get a login, it's perfectly legitimate to restrict access beyond a single access.
However, I just tried what you described and was able to view multiple members pages without any issue.
[edited by: incrediBILL at 4:57 pm (utc) on June 8, 2008]