Right now, when you're editing a document in multiuser mode, you're going to see changes made by all users. This can be confusing and disturb the user on focusing on what he's going to type. One solution could be to freeze the document and allow changes to be available only after a specific user saves them. That's just one idea, but anything else can be taken into account to improve the experience and let the single user focus on what he's typing.
Not seeing other users edits is technically not possible, as there is a single document view for all users. At the same time, improving multiuser experience is important, see bug 115660 on such an idea, and feel free to add your thoughts there. I'm closing this as WONTFIX, but if you have further suggestions, you're welcome to open another bug report.