This is a live blog post from the SharePoint 2009 talks Las Vegas by Umesh.

How is a service attention used and how does it work?
Features such as web parts use service applications. Really a web attention is getting hooked up to a service attention proxy which again connects to a service attention. Such a connection can be managed individually or in groups. Typically a user comes in through a browser that will request a SharePoint page. Assume that the page contains a search box. The user types in a query and the request goes to the attention server. SharePoint uses it’s own load balancer algorithm to route it to the right attention server.

What happened to SSP?
When compared to the MOSS Shared Service Provider we can say that the services still exist but have been unboxed and don’t have dependencies to each other. Also there are a lot more services. And the platform of these services is open and extensible. Next to that there is an integrated administration model, so the Shared Services Admin site is gone and the existing services like Search and Excel have become service applications. The BDC has now become the business connectivity service. So, the takeaway here is that 3rd parties can build new service applications. In whole there are now around 20 services, and service applications that ship with other harvest like Office Web apps, Machinate Server, SQL PowerPivot (Gemini).
Some of the services will work cross farm like the metadata services. Between farms there should be trust based security. So you will need to exchange certificates between the farms. And finally all services use the WCF foundation to communicate through web services with each other and all services have there own database.

Demo 1
From Central Admin you can manage the services, make new ones, attach them to the defaulting attention proxy or a new one. After that you can go to the servers overview page and stop or start services per server. So, how to use the app proxies? Go to the web attention page and configure the service attention associations. You can also manage that in more detail called the service attention friendship page where you will see the web apps and the service proxies. The defaulting proxy is used by all web apps and by all service apps.
The Publish button is there to publish service apps to other farms and the actual connection type the service app is by like https or net.tcp. For the other farm to learn the service you will have to send a special URL that you can see on the page. You need to have established trusts and users enough permissions to consume the service to make this work.

Managing a service
You can now delegate a service to a dedicated administrator. So now you can have someone who can only manage the search. For most control you can use Powershell orders to make service apps. From the admin page you can make, edit, delete, connect to remote service apps and publish and secure service apps. There are also admin pages related to the search apps like the search dashboard where you can see the search crawls, status etc.
Large companies would probably make a services farm and other farms consume services from that farm. Example: service farm provides search, user profiles, BDC and the farms that consume are My sites, team sites.

Check it out:Serve’s Sharepoint Blog