Second, unlike SQL Server, the third-party backup solutions have object-level restore, which can come in very handy in a number of situations. If you go with SQL Server's Backup Compression for your enterprise servers, you're losing functionality.

Third, the third-party solutions have centralized repositories and provide centralized reporting and alerting. So if you use SQL Server's native compression, you've effectively eliminated centralized management of backups for those boxes.

There are other features that third-party backup solutions bring to the table, but incomplete coverage, object-level restore, and centralized backup management are the biggest reasons that SQL Server's Backup Compression isn't going to be viable for most shops.

Index improvements

Indexes have received an overhaul. Not only can indexes be compressed in SQL Server 2008, but you can also build filtered indexes. Filtered indexes have a "where" clause, allowing you to partially index a large table. This may not seem very useful at first, but there are situations where it's very beneficial.