Hanging after Login's Password Entry

Several users are reporting this new behavior:

MBP of various 2010, 2011, and 2012 versions running fully patched Lion. They go home, with their computers off. They open their computers, power them on, it brings up the username and login box. They put in their password, hit Enter, and the system hangs on a blank screen. Hangs for 20+ minutes, they have to force power off the system sometimes and try again. No error message, no invalid password shake, just.. hangs.

All computer have Mobile accounts enabled and are bound to our Active Directory domain. All of these computers have worked fine for the past 6-10 months, and only recently have had this problem. When a Mac user stops by my office the past 2 weeks, I know what they're going to complain about before they open their mouths.

My guess is that when they're home, they're not on the corporate network. So it's trying to authenticate their password without having any access to the domain server. They do not have this login issue when they are at work.

Nothing has changed on the corporate side. Console logs are not helpful on any of these machines, they don't seem to provide anything that I can search on for a solution.

Any ideas?