1. Are you able to register retail keys through Impulse (Like how you're able to with a few games on Steam?)
Yes
2. If yes to question 1, is there a list of games that you can register retail s/n's around somewhere?
I think Stardock published games are teh only ones using the system right now.
3. Are there weekly special deals, or anything like that?
Often there are
3. Does Impulse change the "stock" directory of games, like how STEAM does?
Impulse has an option to set your own installation path.
4. Does Impulse interfere with User Mods and/or Modding Games in general?
Nope.
5. How's bug support?
Very good