Thread contents not viewable to guests, pros and cons?

I currently have a promotion where new members get upgraded to "Premium" after 5 posts. However have you guys tried turning "Thread content" viewable to members only? Forcing guests to register to see thread content?

Has this boosted your member numbers at all? Any pros and cons? I'd assume it would like Google out of indexing content?
 
I'd like to be able to do it by thread
Eg I'd like to post a thread that my members can see
But I don't want guests to be able to see it.
(I have some keen oppositon to my forum)
 
Back
Top Bottom