There is a natural bounce and play on the end of the boom, which largely settles out, but can also be minimized by additional tensioning on the boom, as Steve suggests with ropes. I'd use two come-alongs, if possible, to pull the boom towards the body or other fixed objects if you need long exposures (imagine a V shaped tensioning rig). It is a lot more time consuming, but you can actually set your lengths and then go up and down without adjusting them as long as someone below pulls the guy ropes or cables away as the boom lowers. When you go up again, max the boom out against the guys and you will be more stable and in the same position as you set it initially. If the hydraulics are tired, though, you will have to reset the boom from time to time.
Overall, it is a little like getting used to being on a sailboat in one of these baskets and you need to get your comfort level up as you get used to the jerky movement on the end of the boom. I don't mind it after a couple of minutes, but it isn't for everybody.
-Ron H.