Members have the ability to change how many posts they see on a single page; guests have to make do with the default. Consider another incentive to sign up.
To change this amount, click on "Edit Profile," which is located on the Control Panel on the left-hand side.
Scroll to the bottom of that page. You'll find a tab labelled "Forum posts per page." You can change this value to 10, 25, 50, 75, or 100. Once you've picked whatever value you want, click "Save Changes," and you'll be all set.