While Google awaits FTC approval for their AdMob acquisition, Apple is moving full steam ahead on their own ad network called iAd. It is going to be very interesting to see what Apple can do with their offering -- in my opinion, it's actually going to be kind of hard for them to gain some footing.
There aren't many things that Apple completely fails at -- when it comes to consumers anyway. However, iAd targets a completely different crowd with high standards -- including a really good and established channel, powerful tools to measure their success, and cost effectiveness.
Apple is proposing an ad network that is highly interactive, and emotional -- that means ads need to be very rich, and have a lot of thought and effort put into them. If their app approval process is any indication, posting an advertisement to their ad network isn't going to be as easy as a similar Google offering.
Google makes it really easy to create an advertisement -- two lines of text and an icon if you want. To have an advertisement on iAd, it sounds like you're basically going to have to create a complete application to even have a chance of showing up inside apps.
As an advertiser (especially one whose budget helps make up the long-tail in online/mobile spend), would you really choose iAd as your advertising network if it takes a month to create an ad that will be approved? I would stay with a network that gives you instant gratification, personally. We will see what happens when the dust settles.