I've noticed that when using MDT 2010 and USMT 4.0 that certain items I believe should be migrated such as mapped drives and network printers aren't. Is this right?

Contributed By: Cliff Hobbs [MVP ConfigMgr]
No. Although this should work "out of the box" unfortunately it doesn't. The problem is caused by the Ztiuserstate.wsf in MDT 2010 having an incorrect working directory specified.  To get this to work as you'd expect it to you need to modify this file as detailed Microsoft KB Article 977562 "Network drives and network printers are not migrated when you use Microsoft Deployment Toolkit 2010 with the User State Migration Tool (USMT) 4.0"