The fact that Google AdWords rewards relevancy creates a big differentiation for Google AdWords over Overture's system. The simple fact that your ad position is determined by the combination of your bid and your click-thru rate causes you to focus on the right things:
When you try to over-think the buying of PPC ads, you can get distracted by complex bid-management strategies such as day-parting: choosing when to run ads in order to reduce cost.
Although Overture's transparency has some advantages, it's all too easy to get caught up in the bidding process, since the bids are all that control your ad position. Techniques like day parting may make sense for high volume sellers who have very good understanding of their demographics, but for the most part, it's a distraction.
There are better ways to spend your time if you are looking to maximize profit on an ad campaign. Consistently focusing on keywords, ads and landing pages can easily increase conversion rates by factors of 2x or 3x.