Hi,
I was thinking it would be good to support having velocity vectors in directions other than the direction that the camera is facing.
Right now, it would appear that if you are in "Free" mode (ie. no tracking or following) and have a velocity set, you will always go in the direction you are facing. It would be neat if instead you could set your velocity and then reorient the camera without affecting where your actually going.
With the gravity patch on the development forum, an even better idea might be to add the ability to set accelerations rather than velocities. So, for example, pressing the down arrow key would have the effect of firing a rocket pointed in the opposite direction of the camera. But once you release the key, you can move the camera without changing the direction you are moving in.
Basically, it would be really neat if Celestia had a mode where the camera behaved as if it were mounted inside a spacecraft with thrusters, and you could control the motion of the spacecraft and the orientation of the camera independently from each other.