Now that SLRs are video capable, it becomes necessary to practice more skills. One that can be especially useful is panning. First, whenever possible use a tripod. You will have more control and a smoother result.
The actual speed of panning though can take some practice to find the right speed. This speed will vary somewhat, depending on what shutter speed you are using. Too high of a shutter speed and your video will look choppy if you pan too quickly. A similar problem can occur at some of the slower shutter speeds- moving too quickly and the pan will have too soft or a blurred feel to it. You have to be careful though, pan too slowly and the audience will get bored withthe pan and wonder when you will get to what you are panning to or for.
So practice, find that balance between blured or choppy and boring. It will be worth it in the end.