While I've seen this in several forums, it is a cool trick that doesn't seem to be that well publicized.
If you're planning on reinstalling Deployment Server and don't want to research all your existing licensing info when you reinstall (and who, pray tell, does?) this tip's for you.
If you are planning on reinstalling Deployment Server, first make a copy of the express.exe from the old installation, rename it to express.lic and set it aside.
Once you have reinstalled DS, copy that express.lic back onto the machine. Use Product Licensing Utility to point to that file and all of your licensing will be exactly the same as it previously was. No need to hunt down the old .lic files used with the original install.
Comes in very handy when some of those old files are missing like I ran into several weeks ago. Hope this helps someone like it helped me!