Right now it looks like the MSDN servers are being crushed by the number of people trying to download:

For Windows 2008 the highlights are:
-Significantly improved performance of IIS
-Built-in virtualization (Hypervisor)
-Faster file sharing (There have been many good benchmarks on this one)
-Introduction of the Core edition (A stripped down command line only version)
More information about the Windows 2008
For Vista SP1:
- 50% improvement of network file copies. (Sure hope this is true)
- Resuming from sleep mode significantly improved
- Many common causes of crashes addressed, and fixed
- Faster RDP sessions.
Some more detailed information from Microsoft:
Notable Changes in Vista SP1
Overview of Vista SP1
Posted By: Steve Wiseman on Tuesday, February 05, 2008
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