I love the Nostromo - been using it pretty much since it came out.

I have a druid/priest setup currently, with my druid as the main. I have all the keys mapped in game for my druid, and then I use CTRL+hotkey to control my priest in tow. I'm using Synergy hotkeys so that I can translate keystrokes from my main to my secondary. My key binds are exactly the same on both toons so that I can switch from one screen to the other and everything works exactly the same.

The bonus of this is that since I'm used to playing a priest as my main toon I can utilize the priest completely for both offense and defense. This gives me two fully functional toons versus one just being relegated to a pure support role.