Recommended shutter speed for focal length is 1/focal length.
eg. for 200mm, recommended shutter speed should be around 1/200 or faster, so if you wish to go for lower shutter speed due to low light conditions, you might want to use a tripod.
Correct me if I am wrong..
Depends on your shutter speed and handholding ability (i.e. how steady you can hold your cam). Shutter speed equivalent of 1/focal length is just a rough guide of what shutter speed to use to ensure that blurness caused by handholding would be cut down to a minimum, but it varies from person to person. In any case, to get really sharp pics at focal lengths 200mm and above, a monopod or tripod is definitely recommended. Handholding at that length is fine, but probably won't result in completely sharp pics (unless you switch to burst and probably one or two would be sharp enuff).