Interesting: I was trying to think of a way to do just what you are talking about and a thought occurred to me. If you create a new group with guestlike privileges, you could restrict their access as you see fit.
Let me explain; my application is for a church that has several types of members. Religious forums are difficult by nature and then you throw in a few extremists and it gets, well, colorful. I have 10 moderators who help manage this unruly crowd but because it's a church supported website we can't just ban every person because they can't hold their temper. So we have 'levels' of banning.
First, a 2 week time out where they can read and not post
Second, a 30 day time out where they can read and not post
Third, a year time out where they are not supposed to have access.
Forth, permanent. This is reserved for most extreme cases.
Using the group feature of WWF, this may be much easier to manage. That's a good thing.
I'm still waiting for the new version before I mod the basic forum too much. I'm hoping that groups are managed differently in that I can assign multiple groups to individual users. (Such as participating moderators etc.)