Good afternoon, Sean!
I've been able to print maps just using the tools in Silverlight 4. There are no special ESRI functions for printing that I'm aware of.
I have a sample project that just does printing, if you'd like to have a look. I tried to upload it, but even zipped up it appears to be a bit too big.
Reply with an email address I can reach you at, and I'll fire over the project.
Thanks!
Lisa Chesley