If vBulletin.nl would be introducing paid subscriptions, what do you expect them to be used for? I am curious! (hypoth. question)

Perhaps for priority support. Certain members could be guaranteed answers/help on problems within a certain period, or something.

Possibly more PM storage space, larger avatar size allowence, and stuff like that.

So you would use paid subscriptions for ehm... special permissions/abilities that normal users don't get. That's what certain forums do and it's very successful, for both the owners and users.