What might be interesting is to create the possibility of access to sub-parts of the forum, based on the number of posts a member has. 

One could for instance use the user groups and user access levels in joomla to achieve this. It would require the same mechanism as is being used in the ranks, where one can set a post count to a rank. 

as soon as this post count is reached, the uses could be changed to a user group with a different access level on the forum sub-forum or even an extended view in the Joomla Structure of the website. 

Where is it good for? 

Well imagine that you want to restrict part of your forum only for regular visitors and a bit more reliable posters, then you could lay a barrier on this part of the forum for instance at 5 posts. Every occasional registering visitor, who is just curious will just see the normal parts of the forum, only after he has posted 5 posts, he suddenly gets access to the more restricted part of more regular posters. This will separate the more serious poster from the passing by poster. 

On could even think of an even more extented bonus for posters with e.g. more than 50 posts. I have seen this on other forums and it appears to be very convenient. 

Cheers, 

jim