Anyone working with Visual Studio "Orcas" to build mobile applications should be aware that the v3.5 Beta 1 Redistributable are now available from MS Downloads. There is also a good list of the new features that have been added to v3.5 of the .NET CF.
If you have been following Mark's blog and have been wondering why the WCF over Email sample doesn't work you will be relieved to know it's not just you! The redistributables are NOT the same binaries as what comes with the Orcas B1 installation/VPC. The redistributables actually contain a fix as documented on the download site.
The beta1 build of the .NET Compact Framework which shipped in Visual Studio ‘Orcas’ Beta1 does not allow for any project referencing Microsoft.ServiceModel.Channels.Mail* dlls to be compiled. If you’re using Orcas Beta1 and you need to build using these dll’s, first uninstall .NET Compact Framework v3.5 beta1 then download and install this version of NETCFSetupv35.msi.