Well, the Imperial Edition DLC is not working for me at all.
I can't seem to find the golden dragon skin that is supposed to come with it anywhere. A thread I found on the Larian forums suggested that you needed to have the game patched in order for it to appear, but my copy is patched, so I don't know what's going on.
The Dragons on Earth map is also missing.

Any ideas on how to fix this?

EDIT: OK, I figured out what it was. On Win7, the DLC installer needs to be running under an admin account in order to work, but I'm playing on a non-admin account. And, for some inexplicable reason, the DLC will only work on the admin account it was installed under...
Why? Why, Larian? Why would you code it that way?
*sigh*

So I solved the problem, and for anyone else who's experiencing it, here's how:

1) For both user accounts, open My Documents/Larian Studios/Dragon Commander.
2) Copy the folder named DLC from the admin account into the normal account.

Boom.

Still don't understand why Larian made this an account-dependent feature...

I was confused about the same thing, the solution here worked for me. I'm in Windows 7. For any of you who are logged into admin accounts on your PCs all the time, do you even lift, bros?