Click on the drop down arrow next to your screen name and the select "My Settings".
On the settings tab, which should come up first, and scroll down a bit, you will see a drop down box like this:
your other option, is to Show you all content you haven't read...
Another option:
If you click into the search pane in the upper right (just below your profile pane), click the drop down and select 'forums', then click the magnifying glass.
The results will be sorted descending by update time (as opposed to original post time) so they may appear out of order, but aren't.
