You will get an arc/spark from which ever pole you disconnect first, and as Keoke points out, only if you have a load on the system. You will also get an arc when reconnecting, even if no load, as the battery charges the capacitance of the wiring/system of the car. It won't spark again if you disconnect/reconnect though since you've already charged the system, unless there is a load on the system like the newer radios which syphon a little off the battery to keep the memory/etc. energized.
hope this helps, having problems??