So, I've never used vBseo, and I don't have any plans on using it - so with that said, how many users here have used this software for their vBulletin forum? How was it? Did you see a traffic increase due to the organic urls and such, or?
If your site is small it seems okay The larger forums will cause issues on server resources. This was the reason I dropped it on my other forum last year.. It was either that or upgrade my server.
In the simplest terms, it's causing the server to do more things (rewrite the url's - all the additional stuff vbseo does) so it's going to have an effect on performance.
I agree with Brandon. I think VBSEO is something for those looking to make money. And with that said you should not be reinvesting into your forum till it is making money. VBSEO is a great product, but if your site is not paying for itself then I would not add it. It is all about the balance of an admin to keep the members and the site progressing without digging a moneypit. Obviously, VBSEO does more so it will use more resources. So, your going to need a better server. Which costs more money. And if your not making any money, then your going in pocket. As for as its features and how well it works, I think it does a great job. But, I do not think it is for everyone because not everyone makes a forum to make money.