what's the difference betweet sql 2008 and sql 2008 r2

http://www.microsoft.com/sqlserver/2008/en/us/editions.aspx

http://social.msdn.microsoft.com/Forums/en-US/sqlsetupandupgrade/thread/0be511b2-0c21-4206-90ee-8ce214285a3a/
http://msdn.microsoft.com/en-us/library/bb500435%28SQL.105%29.aspx

 http://blogs.techrepublic.com.com/datacenter/?p=2715

PowerPivot for SharePoint

PowerPivot for SharePoint adds shared services and infrastructure for loading, querying, and managing PowerPivot workbooks that you publish to a SharePoint 2010 server or farm. To create PowerPivot workbooks, you use PowerPivot for Excel.

PowerPivot for Excel

PowerPivot for Excel is an add-in to Excel 2010 that can be downloaded from the web and installed on client workstations. You use PowerPivot for Excel to assemble and create relationships in large amounts of data from different sources, and then use that data as the basis for PivotTables and other data visualization objects that support data analysis in Excel.

Multi-Server Administration and Data-Tier Application

The SQL Server Utility forms a central repository for performance data and management policies that tailor the operation of instances of the Database Engine that have been enrolled in the utility. It also includes a Utility Explorer for centralized management, and dashboards that report the state of the managed instances. A data-tier application (DAC) forms a single unit for developing, deploying, and managing the database objects used by an application.

Master Data Services

Master Data Services is comprised of a database, configuration tool, Web application, and Web service that you use to manage your organization's master data and maintain an auditable record of that data as it changes over time. You use models and hierarchies to group and organize data to prepare it for further use in business intelligence and reporting tools, data warehouses, and other operational systems. Master Data Services integrates with source systems and incorporates business rules to become the single source of master data across your organization.

Features Supported by the Editions of SQL Server 2008 R2

The largest database supported by SQL Server Express has been increased from 4 GB to 10 GB.