If it's Trebuchet (which is all over a2k btw) it's much bolder than normal methinks.
Isn't A2K's font Verdana? I'm pretty sure, but you appear to have hidden the stylesheet from us mortals (templates/Able2Know/Able2Know.css).
The main font is, but quoted text and some navigational elements are Trebuchet. The typography on this site is horrid so don't expect it to make sense.
Yeah, now that I know what to look for I'm seeing it everywhere. ("Post a reply," for example.)