All I know that is out there is vBulletin. They're simply the best, no doubts, no questions. They don't give you bullshit, outstanding customer service and they take their customers as serious as their security.

But there are others trying to catch up and even surpass vB.

Invision Power Services with IPB
And GroupEE, form. known as UBB

Are there any serious ones on the ASP market?
Who else is there on the PHP market?

Is IPB catching up by introducing new official addons like their announcements make us believe, or shouldn't vb customers worry.

personally, i do not.. why? Because i dont need all that extra stuff. :)

I think that there official addons are a great leap forward. Personally most other boards I have seen are behind vB in terms of functions.

Also, for me one of the most important things about a forum is its layout. vB is very intuative and i don't have to hunt for things. But with other software I have to search and when I find it I can't think why the developers put it where they did.

Kind of like the dashboard layout on the last model of the BMW 7 series. :(

phpBB is one too. I think phpBB is pretty big just for the sheer fact that it's free. When you compare $160 to free, it's a pretty big difference :) I don't think phpBB is really close to the quality of vBulletin, but the price is certainly right!