also don't let people quote 4th ed rules to you.
5th ed. The only models that actually move are the models that will be under the tank when it stops or those that fail their moral check and fall back.
And You must declare the distance of the tank shock before you start the move.
I use it to make enemy models step slightly away from the 3" ring around the objective.
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Another thing to remember with 'Tank Shocking' is that you are able to ram your opponent's vehicles, and cause damage/destroy them. Not many people remember this rule, and I once used this to destroy my opponent's Leman Russ with my Land Raider. The look on his face was priceless.
There are several things that tally up to give you the strength of the hit.
For every point of armour over 10, you add +1.
For every full 3 inches your vehicle moves, you add +1.
If you are using a tank (as opposed to a walker), you add +1.
You then add the roll of a d6, and that is the total strength of the armour penetration roll.
The enemy tank adds up their strength as well, but since they don't get anything for not moving, their armour penetration roll back is often pretty weak.
A great one to pull out on the unsuspecting.
Tank Shock is also great for forcing those leadership tests and forcing Marines off the table. Especially if you keep chasing them so they can't regroup.
The strength modifier for distance moved applies for both the ramminng vehicle and the target vehicle (P69 example left column next to last paragraph).
I have seen rammings where both the ram and the target vehicles had the same strength, although usually somebody only rams if they are at an advantage.
It was added to give weaponless rhinos something to do. Also realize that orks came out coexisting with 5th ed and they use this rule heavily with reinforced ram and especially deff rolla. For other armies its just another option, say you have a chimera with multi-laser or other low strength weapon. You need to destroy a tank so now you tank shock. You may take damage to a low value apc but you might also destroy a high priority target. And against small ork squads it is devastating. I once lost two squads of 6 and 8 lootas when they where camping at the back to fire long range and a chimera drives up and they fail tests. Two squads at about 220pts both run off the table.
I'm surprised no-one has mentioned being able to reach units hiding behind other units yet. Say, for example, your opponent is playing Guard and hiding his command squad with 4 Plasma guns behind a squad of infantry amigos. You have a Tactical Squad of marines in a Rhino. Rather than smash the infantry in assault and get rapid fire plasma'd to death in your opponent's shooting phase, tank-shock the infantry and assault the command squad. With luck and intelligent use you may be able to combined assault both units.
Great use for empty trukks (w/reinforced ram), especially against low-ld armies like guard or Tau. I'll tank shock anything and everything just to have something to do.
Tank shocking deamon units with the deffroller is probably one of the most fun things I've done in a long time.