Nothing quite like cutting it fine on the naming still being valid :-)
Get all the info and downloads from here. A quick scan reveals the following improvements;
T-SQL - Separate Data and Time Types FINALLY, YIPEEEEEEEEEEEEEE
SQL Server 2008 introduces new date and time data types. The new data types enable applications to have separate date and time types, larger year ranges for date value, larger fractional seconds precision for time value, time-zone offset aware datetime type that containing date, time and time zone offset portion, user defined option on fractional seconds precision of time related types and datetime2 and datetimeoffset provide standards conformant semantics. Along with the T-SQL support on the new types, both native (ODBC, OLEDB) and managed (SqlClient) providers also provide the full support through the client driver APIs.
T-SQL - Object Dependencies
The object dependencies improvement provides reliable discovery of dependencies between objects through newly introduced catalog view and dynamic management functions. Dependency information is always up-to-date for both schema-bound and non-schema-bound objects. Dependencies are tracked for stored procedures, tables, views, functions, triggers, user-defined types, XML schema-collections, and more.
T-SQL - ORDPATH
ORDPATH improvement provides an important new functionality to our customers who use hierarchical data. It provides a superior way of modeling hierarchies in SQL Server by introducing the HierarchyID system data type and corresponding built-in methods which are designed to make it easier to store, query and operate hierarchical data. HierarchyID is also optimized for representing trees, the most common type of hierarchical data.
T-SQL - Large User Defined Types
Large user-defined types allows users to expand the size of defined data types by eliminating the 8‑KB limit.
Reporting Services - New Server and Designer
Improvements represent the two major infrastructure changes for Reporting Services. Reporting Services enhances the processing engine and rendering extensions to enable new functionality, such as Tablix support, and scalability as well as remove the dependency on IIS. Additionally, new report designer and configuration tool are provided that improve usability and workflow for RS customers.
Management - Performance Data Collection
Collect data from various sources in SQL Server and OS to help with performance troubleshooting and server maintenance. With this improvement, organizations improve their analysis of common performance issues:
HADR - Database Mirroring Enhancements
SQL Server 2008 builds upon the momentum of SQL Server 2005 by providing a more reliable platform with enhanced database mirroring: