I upgraded some of my forums to IPB v1.3 which is also SE friendly and I've noticed an increase in traffic. You'll get a lot of hits from odd keywords that you don't target, but someone posted in your forum.
What mods have to be done? Or should I switch to the "search friendly" options? The forum is fairly new and doesn't have much activity yet. Thanks.
although vb3 is "search engine friendly" (meaning it doesn't use session-ids in the urls), it isn't completely optimized either. there are a bunch of optimization hacks available at vbulletin.org
Agreed, you can do things with mod_rewrite to make your URLs no appear dynamic or make them keyword rich, but for me, none of that was necessary.
you've got a decent PR to the forums, though, so I think the fact that you have those query strings don't matter much. if your forums are like a PR3 or PR4, I'd imagine it could have a huge, huge impact on the number of threads cached though. and if you've got really big forums but are concerned about SE's chewing up bandwidth, you can always disallow all but the /archive/ because those pages are very lightweight and completely optimized.