@Ryan - hat makes any other forum software as good as bbPress?

Nothing, they are already about the same... (We're speaking about on-page SEO qualities.)

Sending trackbacks help as it automatically posts links to the forum on other sites.

...expecting they're using bbPress (or WP blog) and they didn't disable the feature. Other side most likely uses rel=nofollow on these links so their benefit for our ranks is... is?

Acquiring evidence of the effects of SEO is difficult and I doubt anyone has tried to quantify the difference...

Sure, I form my opinions by opinions of SEO experts, that is the kind of evidence I'd like to see.

the SEO benefits of trackbacks, semantic HTML and pretty permalinks is well known
IMO, they might be well believed by WP community, but I wouldn't say that they are well known and I would say they are overrated. About the keywords in URL, well, these probably matter. But how much? http://www.seomoz.org/article/search-ranking-factors