Sorry to bother with such a simple question, but I’ve done a lot of searching and there doesn’t seem to be any information about this; which may mean it’s not possible. But I do a lot of switching from machine to machine, and I’d love to have my personal user interface and prefs on a thumb drive that I could just plug in and load into Blender. Something like my own user config file that I could load. I do this with a few other apps, but don’t know if Blender allows this.
Just save your startup.blend file (assuming you are talking about blender 2.56, earlier versions use a different file). Its location is dependant on your operating system.
Or just open blender and save the file. This will includes your preferences. Or just save blender and the startup.blend file on a usb stick so you can take everything with you including any 3rd party addons.
So, will this work with another blend file that I’ve been given with a scene already set-up? if I’m given a blend file that someone has set up for me, and I want to change the interface to one that I’m comfortable with, I first open my own saved blend file with my prefs and then open theirs?
No, just uncheck the load UI button/box when you load the file. Then you will have your default UI.
Perfect! Thanks so much 
-Cheers!