Although I do think I understand the rules for saves against movement, I don't really follow them in my games.
I think that controllers often don't get their time to shine as easily as othe classes, particularly at lower levels. A fight on connected bridges over a lava pit should be their time to shine.
On the flip side of this, I also don't want them to ruin the fun of the encounter entirely. It is not very epic to have the BBEG thrown off a cliff to his death with one spell. I am yet to read a book or see a movie were the important bad guy was thrown off a cliff without a great fight first. (...Stupid Balrog/Gandalf, proving me wrong...)
I use the following rules generaly:
- Neither monsters nor PCs get a save against anything that is not 'really deadly'. If you don't want to get pushed into a fire, don't stand near it and don't get hit by the pushing attack. The save represents plot-armor for both monsters and PCs, so only counts against things that will kill you, not hurt you.
- Bloodied/blinded bad guys get -5 to their saves
- If you make a save you are prone. If you were bloodied you are also dazed.
- Often I declare that the target that makes a save is clinging on for their life. So every attack until they move now has a chance to send them falling to their death.
- Minions get no saves
- Elites get an additional +3 to saves
- Solos can't get pushed to their deaths until they are bloodied. Then they get +3. Even when they fall, they almost always cling on for one more turn, while the rocks give way all around them. My players love it when everyone has to jump in to finish pushing the guy off the edge.
This allows me to ramp up the difficulty of encounters sometimes, while at the same time ensuring that the fight does not drag on too much. PCs try to quickly bloody the big guys while the controller slaps around the rest, before finishing off the tough ones.
<edit> On a side note, are there any rules about pushing/sliding/pulling huge monsters less? It feels like there should be, given that dwarves are pushed -1 square. My group and I feel we might be missing something when the controller knocks a gigantic creature 5 spaces.