I've just installed the SMF forum and it is far away from being SEO friendly! Having had my site problem free for the last while I'm suddenly getting duplicate title tags, short meta description warnings and even a 404 not found error in google webmaster tools! I also need to create a sitemap for it which is going to be a problem for me.
The structure of the site is beyond my understanding at this point so making changes is hard.
In the case of the short meta descriptions, the reason is that it uses the page title for the description. It's going to take me weeks to figure out how to change that.
Appart from SEO problems it seems to be fairly good but I have nothing to compare it with.
Ian.