Unlike blogging software like WordPress which usually feature good on-site SEO even from a default install, forum software typically has never featured good on-site SEO features. Default themes with nested, non-semantical tables, inappropriate use of headings, lack of any real attempt to use semantical code and appalling use of permalinks are standard features of off-the-shelf forum software.
However, unlike it’s more bloated counterparts, bbPress has extraordinarily good SEO features straight out of the box. The only other forum software I know of which is capable of doing Pretty URL’s/permalinks straight out of the box is Vanilla. There is a free MOD available for SMF which accomplishes this, but for vBulletin this requires a paid MOD.
Another major SEO feature which a default installation of bbPress is capable of is pingbacks/trackbacks. No other software is able to do this by default. There is no MOD currently available for SMF to do this and (again) vBulletin requires a paid MOD to to add the same feature that bbPress can do by default.
The default bbPress theme (Kakumei) features fairly semantical code which has led to most of the bbPress themes available featuring a high level of on-site SEO in comparison to their larger competitors.
bbPress is much maligned by it’s competitors and the average Joe web developer seems to dismiss it as being too basic and “not really useful for anything”. However they are missing the real point of bbPress. It may be a super simple forum system, but although it is lacking in whizz bang features which it’s larger more bloated competitors have, it does include extra more complex features under the bonnet which many do not realise are there.
Having said all this, I actually use SMF myself. Both my support forum and my site about Hockey in New Zealand run SMF. The reason I don’t use bbPress for either of these forums is because it would require too many plugins and the workload required to create a custom theme of high enough quality is simply not worth it. Some basic features I would like to have available in my forums are not currently possible with bbPress without considerable effort.