I've been developing reporting solutions with Micosoft Analysis Services (originally called MS OLAP Services) since it first shipped with SQL Server 7.0.  For the last two months I've been working on a contract at Microsoft using SQL Server Analysis Services 2005 and must admit I'm highly impressed with the product.

There are many improvements to the newest version of Analysis Services.  From an application interface point of view, I'd have to say that the integration with the Visual Studio 2005 environment was a great move.  A standardized interface for all of the SQL Server components (Database Engine, Analysis Services, Integration Services, Notification Services, and Reporting Services) is pretty nice.  I like being able to run queries against multiple databases as well as cubes within the same window.