As far as I can tell, the profile pages only show comments, discussions etc... for that particular profile. If you have a link to a profile that is showing all site-wide comments, discussions etc.. then we can check it out. I'm not seeing any issues on my dev site.
In your "Settings" tab, if you have the enable categories checkbox checked, you'll then need to create the categories you want topics for in the "Categories" tab.
If you don't want categories, then uncheck the enable categories checkbox.