Plenty of content continues to get produced for WSE 3.0. Working with Ron Jacobs and Don Smith we produced some ARCasts on WSE and X509 certs that you can be listen to here. All of Ron's ARCasts make avid listening to, especially in the car on the way to work (download and burn onto a CD). You can also find kerberos versions published here with username and password best practices usage coming soon.
Next month in the April 2006 MSDN magazine Aaron Skonnard has a great article on WSE 2.0 to WSE 3.0 migration. Combine this with the WSE 3.0 docs and this migration video sets you up well to understand how to migrate your code.