The default font for the SDMB is Trebuchet, one of the faces Microsoft developed for web display. It was once available for free download in the past, but no more, perhaps because it is now bundled with either the newer Windows OSs or many Office applications (somewhere in MS’s website there is a listing of what fonts are included with what Windows apps, but I can’t find it for the time being…).
I’ve heard the studies, but I still think that serif fonts look to squishy to me and they tend to blur together with bad xeroxing.
Personally, I’m a big fan of Trebuchet MS. I have it set as my default web page font. It’s spacious making it easier to read and there’s a small semi-serif-like hook on the bottom of the lowercase L distinguishing it from the uppercase i.
OTOH, Trebuchet is just okay in print, but Palatino is truly beautiful. I can appreciate that.
Bottom line, variety is spice of life. 
Doh, how did I miss this post to begin with? I would never have realized that my new fave MB defaulted to my own default fave font…great minds, huh? 