SQL Server 2008, aka "Katmai," gives SQL Server shops plenty of reasons to get excited. The best SQL Server release to date, it sports more nice new features than you can count, and the improvements extend to both performance and manageability. In a few cases, such as the Resource Governor, you'll wish Microsoft had taken the functionality a little further. But whether you manage an OLTP environment, or an OLAP environment, or both, you will most likely find Katmai compelling. It easily passes my own five-point test for upgrades.
My five-point test requires a new release to bring at least five significant improvements to my environment, or it's not worth upgrading. Each improvement has to change my life in a significant way, either by dramatically shortening the time to do common tasks or by allowing me to do something I couldn't do before. For my environment, which is a large data warehouse, these five Katmai features easily pass the test: Change Data Capture, Lookup Cache, Data Compression, PowerShell integration, and Policy-Based Management. And I could easily keep counting.
How does Oracle Database compare? See the review, "Oracle Database 11g shoots the moon."
Change Data Capture and Lookup Cache will be popular with DBAs who want to speed up ETL (Extract, Transformation, and Load) processes, as will the pipeline improvements in Integration Services, enabling it to push data much faster. Data Compression, PowerShell integration, and Policy-Based Management, not to mention Server Groups, should make a big splash in almost any environment. Just keep in mind that the benefits you get from Data Compression (which works at the page level, replacing repeating data with lookup pointers) will depend on the nature of the data in your table and how it's ordered.
Backup Compression is also new in SQL Server 2008. Although the compression itself works well, the feature has too many limitations (including supporting only Enterprise Edition) to be effective in an enterprise setting. Another compression feature, called Sparse Columns, allows you to store nulls without taking up physical space. Sparse Columns will come in handy for large tables containing many null values. It's just too bad you can't use Sparse Columns and Data Compression on the same table.
Policy-Based Management allows you to define almost any configuration or administration policy you might think of for any number of servers, and be alerted whenever those policies are violated. Although spanking new in Katmai, Policy-Based Management already seems mature.
The inclusion of PowerShell will reinvent the way DBAs manage their environments by taking complicated cursors out of management scenarios. This is the debut of PowerShell in SQL Server, and there are some rough spots. But I expect they'll be ironed out soon enough. I've even heard rumors that PowerShell will eventually replace sqlcmd as the command line interface.