I already have a whole set of CSS rules I apply to Facebook now, just to make their UI less awful, remove the massive amounts of crud I never want to see, and resize the few things that I do want to see up from their stock postage-stamp sizes. Blocking .ad-unit or #pagesYouDontCareAbout is easy.
#rightCol{
display:none;
}
#contentArea{
width: 700px !important;
}