Wow that's an old discussion. Depending on the requirements list, $250 can be enough to get it done.
The questions are things like what information should be given by guest users. Can guest users create discussions. Should there be a way to merge a guest user information if they create an account afterwards. Should guests be prompted to create an account after posting. What should happen if there is an actual account with the same information the guest user has entered. Should guest users be shown as anonymous or should they chose a display name. Should multiple posts from the same guest display name be visible on a page or not. Should guests appear in the user list.
Fully anonymous posting is yet another aspect of it.