Hi Binow. You can do tons of fun things with your cnc. Check here on the zone for Meshcam. Robgrz has written this program for taking stl, bitmaps and I believe dxf files and has made it possible to do 3d engraving on any 3d cnc machine that takes gcodes. As far a bobcad goes it is a cad program and you will only be limited by your creativity as to what you can draw for machining. Some programs are better suited for "fun" stuff than the cad programs and there should be someone else tell you what those are.
Mike
No greater love can a man have than this, that he give his life for a friend.