Currently forum columns use mix of percentages and pixels for width and margin/padding, causing columns to stretch at different resolutions and at low resolution break layout.
It was done that way because back then it was impossible to do otherwise because of IE6 and other old browsers.
It can be fixed by setting fixed width to certain columns, with help of negative margins, box-sizing. With minor tweaks even IE7 can support it.
This fix will make forums list (and other similar lists) look the same on all resolutions and will allow to eventually implement responsive design.
See http://area51.phpbb.com/phpBB/viewtopic.php?f=108&t=44139 for more details.