I’ll give bbPress a try. It’s

a forum software with a twist. bbPress is focused on web standards, ease of use, ease of integration, and speed.

to see if it can be useful on my website.
It is still my believe that the forum from is to weak for the size of WP blogging software, lacking more and better user tools like “check my posts”, “view latest unanswered posts”, “subscribing”, etc.