Dani,
Your mod-rewrite is very good but it does leave some possibilties of duplicate content, which could result in Serps appearing slightly lower than they should do.
Would you be willing to re-code this slightly to fix the issues if i was to point out where the duplications are coming from?
I understand the search engines very well but i am afraid i am no good with mod-rewrites & i have been trying to look at your code & see how i might edit it myself but its a little over my head.
The first area is easy to fix & i was able to do this myself, its caused by simple naming conventions in your code - your current code produces two seperate URL's for forum threads. The first is in the latest thread shown on the homepage - the thread's URL is different if you enter by the forum.
To fix this just name this variable the same as thread in forums - easy.
The next two required fixes, i can't do myself.
1) The all posts by user contains an ankor link to the post, but this still uses the dynamic string - it should be the same URL as post ... html#post234 , etc
2) The Forum Jump still contains the dynamic URL's - these should also be changed to html because search engines can follow these links & index them.
I believe that fixing all these should stop any duplications, unless i have missed any scenerios in VB.
The result will be higher pagerank for the forums & higher Serps.