Facebook's FBX enables advertisers using their own data (which could include data from a user's prior Web browsing activity) to reach consumers - when they are on Facebook.
"Facebook hosts the final ad creative and serves it to Facebook users through its [own] servers."
This information is taken from the ASRC's (Feb. 4, 2013) advice on Facebook's adoption of the AdChoices Icon for interest-based ads served through the Facebook Exchange (FBX).
The Accountability Program is an investigative unit of the Advertising Self-Regulatory Council (ASRC)
........"The Accountability Program began reviewing FBX as soon as it was out of beta to determine the roles of Facebook and its approved Demand-Side Platforms (DSPs or FBX partners).
...FBX enables advertisers using their own data, which could include prior Web browsing activity, to reach consumers when they are on Facebook. - FBX is also designed so that Facebook does not gain access to this data.
Further, to ensure that DSPs do not gain access to Facebook's user profiles in order to retarget when the user leaves Facebook, Facebook hosts the final ad creative and serves it to Facebook users through its servers.
This is a change from the general model in which the DSP serves the ad, including the AdChoices Icon."
......This very change (away from the general model in which the DSP serves the ad), is a positive step closer to an eventual (Looksmart) "Web-Wide Ad Network" or, real time search intent based (global) marketplace that I feel, is coming.
With Facebook the publisher (in fact-meaning all publishers in the Open marketplace) signaling a coded IP "ID" of an available impression, this allows other advertisers targeting the search based user intent through Looksmart's marketplace - to compete against those other kinds of (as above) interest-based ads - meaning those advertisers served through the Facebook Exchange.
This is provided (and also assuming it to be the case-in finding a user on Facebook), Looksmart (at all times), get to serve the ads.
This not only protects a publisher's user data (for all publishers across the marketplace), it allows Facebook's own advertisers to compete for these unique- search intent based and very much PLA-like impressions, even when such an impression is available, on Facebook. (Is how I'm seeing it all.)
Disclosure: Long LOOK