I dunno. I mean, I can see both sides of the argument.
On the negative side, it would create a whole lot of work for the person starting the thread, and the members-only part could be kind of off-putting to those not invited to the thread. Further, I'm not entirely sure that it would eliminate the problem of creepy messages and things all together, although it would probably help to some extent.
On the positive side, the main reason pretty much every hot, regular amateur chick has been chased off of here is because a lot of creepers from their real live/whatever have found the site and harassed them or similarly given them a hard time. I'm talking about HBFactor and SugarPie specifically, but I'm sure there are bunches I'm missing. I think such a system could drastically cut down on the random internet surfers stumbling upon people they know/go to school with/etc. and thus perhaps not scare them off. Which would be nice.
Also, I think such a system, especially if implemented to allow only members to see them, could force more lurkers to register (although, I don't really see a reason why they wouldn't have registered for free already).
I think it's a neat idea, and not necessarily horrible, but I'm just a lowly mod - so what do I know.