Nice. Some suggestions, though:
1) Allow us to choose the character directly from the context menu. Right-click -> Audiosurf -> Mono Pro.
Yes, I want this myself too

working on it
2) Not everybody will like #1. Here's when a settings app comes in: You open the app to configure stuff like whether it uses the program menu or the context menu menu. An option to completely turn off the Audiosurf-in-context-menu would be nice as well.
That's a good idea
3) It would be nice if the program auto-detects whether or not Audiosurf has started yet.
Yes this would be easy to build in if Dylan could make it send a ready status with a WM_COPYDATA (like Pwntastic said in the other topic)
4) This is on Dylan's side: It would be nice if it would receive the commands immediately when Audiosurf is running. If you use the application while Audiosurf is on the loading or seizure notice-screen, Audiosurf just ignores it.
It doesn't work at the loading screen but it does sometimes work at the seizure notice. Also working on that