I think is worth bearing in mind that a lot of people are scripting overture now, it was easy a year or so ago. In fact I picked up a quite a few domains, but these days it seems the pickings are rather slim...
The people placing the bids see the bid value in each visitor to their site generated by the search engine. They are prime candidates to buy the domain as they already see value in the term that the domain matches.
But the value is to that advertiser, your own mileage will vary - and pretty wildly.