Thread: Growing the Site
Likely people will link to individual threads rather than a specific landing page per se - now this is correct, because barriers to content drive people away - however what you do want is if the user isn't logged in and they scroll down the page they eventually get "hey you look like you're enjoying this site - here's why you should sign up" - it's something done on the RPS forums I think though they use a different piece of software to do the job.

Yes, makes sense, it does not have to be at the landing page. Perhaps as a stickie message at the top/bottom or something, after having clicked into a few threads?