Last fall, in the article Mike Downen and I wrote for MSDN magazine, we mentioned the expanded support for X.509 certificates, and specifically pointed out how to use them with XML digital signatures.

For those of you picking up the Febuaray CTP (and later) of Whidbey, you'll notice that we've renamed the X509CertificateEx class to be X509Certificate2 in order to comply with the framework design guidelines.  All of the code snippets from the article are still valid; however you make that one simple substitution.