I have gone on about this ad nauseum.
I have seen no evidence that it helps in regard to SEO. None. Nada. Zip. Zilch. Zero evidence.
It doesnt hurt as far as I can tell either.
The software does other things, but its main function is to do a mod rewrite of the URLS.
It was once true that forums had trouble being spidered due to the variables in the urls. But that was 4 years+ ago. vBulletin is spidered and indexed just fine today. The best evidence of that is to look at vBulletin itself. (
site:www.vbulletin.com) 3.6 million pages indexed. I could list a dozen other sites without much effort.
So, if you like the look of the rewritten urls, great. Have at it. But in my opinion, there is little or no SEO benefit to vBSEO. I have seen no evidence supporting the claim that it gets your site spidered easier, or changes your rankings.
For what it's worth, I was offered a free copy, and declined.