Google mobile search ads are a vastly underused channel for brands in my opinion. The good news is this means that at the moment they are a relatively cheap way for challenger brands to reach prospects in a recession.
Even big auto brands like BMW, VW, Jaguar, Honda, Ford, Toyota, Mercedes and Audi are not advertising on Google mobile. Their ads were missing from a quick search I did back in December 08 and again on Google mobile today, despite each having a mobile internet site. This seems like laziness on the part of media planners, or have these brands tested mobile search ads and found them lacking? Not enough search volume on mobile? Maybe they just don't want people to go to their mobile sites? Who knows.
Come to think of it, Audi aren't advertising on "proper" Google on PC at all at the moment, either. They are relying on natural search and not paying for any PPC, so they're excused :)
The only auto brands I could see advertising on Google mobile were Renault and Fiat - challenger brands - and SwiftCover car insurance. Do SwiftCover count as a challenger brand too? Maybe. They were certainly advertising against all the car brand keywords.
While a good channel for most brands, mobile ads are particularly obvious for mobile handset manufacturers, and mobile entertainment brands (mobile games etc). Again, for mobile games it's the new challenger brands who tend to be advertising on mobile (www.lastlevel.mobi), as well as bigger brands like EA Mobile. While mobile handset and operator brands like Sony Ericsson, Motorola, Nokia, Orange, O2 and Carphone Warehouse aren't advertising at all on google mobile. That's just weird if you ask me.
Here's a 1 minute google mobile video with requisite iPhone-style imitation west coast drawl voiceover. Actually, looking at this video I can see why nobody has bothered advertising. Most people have probably fallen asleep by the end.