It's more akin to Orkut, LinkedIn etc but a lot harder to get into. As well as just being invite only, the only people who can invite you are members who have attained a trusted level by becoming valued and active members of the community. It's as much about keeping people out as it is letting them in, and asmallworld.net deliberately want to maintain a low growth rate to ensure that exclusivity.
From both a social and business networking perspective it is, so I am told, a very exciting place to be. Of course, I can't confirm this because they don't give 'review' memberships to lowly tech journalists such as myself :)