Chris Coad at the Complete.com Blog has an interesting summary of Map Provider Market share.

His conclusions:

• Though traffic is down more than 20% from it’s peak in June, MapQuest remains the king of online map services with over twice the traffic of it’s nearest competitor.
• Google Map’s functionality has allowed it to nearly double in size since January 2006. Google’s service is quickly gaining ground on Yahoo’s similar offering, and also shirking seasonal trends.
• Live Search* has been gaining significant traction: coming out of beta in September, it has since grown to twice the size of well established RandMcNally.

He also has very interesting data on the different ways that the services are used.