New for me anyway! Before and after pictures below.
Do you have default settings on SF page sizing?
Click User CP at top of sevenforums page. On the new page scroll down to Edit Options. Click.
New page at the bottom find Miscellaneous Options.
Find Forum Skins. As in left picture below I had SF Deault.
Right picture I changed to SF Aero Wide. Click Save changes.
There is also SF Aero for non widescreen. Also other skin options. Try it and go read some threads. If you don't like change it back.
SF is so much nicer sized properly.