In one of your other HN comments you say:

> Klicknation Inc, for which I am a product manager, is hiring.

>Our flagship product is Superhero City, a Facebook game. You may wonder if a Facebook game can support a whole (small) company, and my answer would be a resounding 'yes'.

So the (non-quantitative) data described by most of the posters here seems to say that there is one type of ad that does seem worthwhile of FB: those advertising FB games (e.g., Zynga, and your Klicknation games).

Of interest would be: who has found FB ads useful for non-FB-dependent products/services?