An estimated 74% of Facebook's US advertising revenue for 2009 will come from local advertisers

"Facebook may “only” make $310 million this year, but a full $229 million of that will be from local advertisers, or 74% of total revenue. That’s quite striking at first, but when you really think about it, a lot of the ads on Facebook are indeed for local venues, and Facebook makes it easy to target geographically."
Source: Identified US Social Network Ad Spending 2009 Projections, Borrell Associates, cited by Mashable, 20th July 2009
Caution - these are projections made mid-year, and also, bizarrely they project that twitter will make $288m in ad revenue, despite it carrying no ads.