Web Services Enhancements (WSE) is a vehicle for Microsoft to get the most recent implementation of the WS-* specifications out to our developers. Eventually, all of the WS specs will be supported inside of Indigo, until then, we bring out these API’s to keep up with the standards process. A good overview on the vision for secure, reliable and transacted web services is available here. The latest release is WSE 2.0 SP2. This release includes a new security token and numerous fixes. The new token supports impersonation, constrained delegation and Kerberos authentication in web farm scenarios.
We have a download available here and updated training on the WSE page at MSDN.