A visual how to I worked on has recently been published on MSDN. The video, Creating Custom SharePoint 2010 Service Applications and Consumers , demonstrates how to create custom SharePoint 2010 service applications for robust, scalable, and fault tolerant shared services.
Microsoft Office SharePoint Server 2007 introduced Shared Services Providers (SSPs) to provide common services to web applications. In Microsoft SharePoint 2010, Microsoft changed this model to use the new service application framework, which no longer groups services together for multiple web applications. This new infrastructure enables more flexibility in managing and using the services. In addition, it is now possible to create custom service applications. This Visual How To demonstrates how to create custom SharePoint 2010 service applications and consumers that take advantage of the service.