Vista Horizons

The Windows Vista Team blog has more details on build 5472 that was released this week:

This build includes quality and performance improvements based on that feedback.
Build 5472 [snip] is an External Developer Workstation, or EDW -- an interim build from the RC1 tree.  I and others think we have made a great deal of progress on improving overall product quality, so we wanted to give a larger group of customers and partners the ability to test and develop on a more recent build.

Additionally, they mention that Release Candidate 1 (RC1) will be shipped this quarter.