Stuff like this just creep me out. I do have an account on Facebook (required for viewing certain albums etc.), but each and every privacy/marketing issue with FB that pops up really deters me and pushes me one step closer to erasing the account.
As has already been noted by people in this thread, FB users really seem to just "tune out" and not notice the ads. My observation is that the people making that observation also "tune out" and don't notice the really scary privacy issue at hand :)
How is this a privacy issue? This exposes no personal information. You could create separate ads with different settings and use the differences in the URLs they point to to connect visitors with demographic data from their profile, but you still wouldn't know their name, friends, etc.
Think of the targeted social engineering attacks you can do with this. If you know that an individual has access to a sensitive computer network you want access to, you can make them a targeted offer they can't refuse and point to a site with some malware rootkit or something. I'm sure there are endless devious tricks that can be pulled with this system, beyond your harmless pranks like these. Now that I'm aware of the possibility that an ad I see is only seen by me, I'm much less likely to trust them with a click.
As has already been noted by people in this thread, FB users really seem to just "tune out" and not notice the ads. My observation is that the people making that observation also "tune out" and don't notice the really scary privacy issue at hand :)