2006 is shaping up to be very interesting from a PPCall point of view.
I think there will a few different areas of interest, local being the one for discussion here but also financial and travel will be huge.
Local PPCall will probably be dominated by companies with 'feet on the street' as getting small, local service-based companies onboard will take huge resources. The number of advertisers will be the influencing factor on who wins in the local PPCall race as technology and other factors will play second fiddle to having relevant ads to monetise.
The other PPCall areas are likely to be dominated by companies that can get their ads on the sites with decent inventory as it will be relatively simple to sign up financial companies etc.