Actually, seo is built in to XenForo. http://xenforo.com/community/threads/vbseo-to-xenseo.367/page-2#post-4969
Yes I know it is, I just dont like it, and my server has a lil problem with it like with friendly urls enabled when people have star symbols in their thread titles it dosent work, so its better turned of.
Most so called experts said friendly url rate higher by search engine. Googl's document also suggest seo friendly urls. When search something in google, many seo unfriendly sites show up. I wonder today's search is so smart that no seo friendly url required.