Google Ad Manager is a hosted ad management solution that can help you sell, schedule, deliver, and measure all of your direct-sold and network-based inventory. (reference)
This new service will give more options for publishers and advertisers to get connected. Before this service launched, Google already has services like Google Adsense and Google Adwords. Unlike these two service, right now Google Ad Manager is not yet open for public. We can apply for an invitation at this moment. Personally, I am interested using this service and I am still not sure whether I will use it for my personal blog or not. But, since I also maintain some other blogs — and some of them have (and will have) an advertising program, I think Google Ad Manager will be a great deal.
For publishers who do not want to deal with complicated advertising management, Google Ad Manager seems promising. Right now, there are some applications publishers can use like OpenX (previously Openads). For some people, this can be a great solution for advertising management. Not only for his/her own site, but when it is used with multiple website. But, as I sad earlier, this probably works for those who have time to learn about maintaining advertisement independently.
Some blogging platform like WordPress also offers alternatives. There are some plugins available. But again, this will work for those who use WordPress.
This service is not open for public yet. But, Google Help Center has many useful information about it. Anyone already got an invitation?