Went to a session by Don Kilen who's a product manager for SQL Server Katmai. Although SQL Sever 2008 will be launched in late Feb 08 with all th eother stuff, expect RTM in Q2/08. Interesting that that only features that they consider shippable make it into CTPs, and this includes the full doco. So I checked this out with the doco download (130Mb) and sure enough there was full doco on the new HierarchyID type, including a couple of lessons.
Some interesting features in the June & July CTPs:
"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."
FileStream data type which allows large binary data to be stored in the file system and yet remain an integral part of the database with transactional consistency
Other interesting features he mentioned are a sparse columns - so that you will be able to have up to 100K columns / table, spatial data types - a flat earth data type (GEOMETRY) and a round earth data type (GEOGRAPHY), and new index types for hierarchies, indexes on filtered values within columns, and spatial indexes.
Will also be improved compression on the fly with not too much performance impact (lots of CPU with multi-cores & I/O still relatively slow), and synchronized programming model (like Outlook / Exchange ? ) and virtual earth integration.