On an unrelated-to-mechanics vein, do many of you Watcher types invoke player limits? It seems like a quick way to put the fear of the doom pool into some players. Obviously, it has to make sense narratively, but I can think of all sorts of scenarios that start screwing with powers by invoking limits, rather than tacking on complications. The nice thing (from my perspective) is that a limit can't be bought off as the result of a great roll bought up with PPs. They are stuck until the Watcher rolls an opportunity.
I tend to activate my players limits when (1) the narrative just screams for it, or (2) when a villain really needs a little help to make the scene interesting.
Example of (1): The Captain America in my party rolled four 1's on a shield throw, adding massively to the doom pool and totally failing his action. I activated his gear limit (he declined the PP, making me spend a doom dice to undo one of his 1's) to have the shield smacked to the floor. It ended up great, as the person playing Echo ended up with Cap's shield and copied a bunch of his moves before returning it to him.
Example of (2): In an attempt to make Electro a little more challenging while outnumbered 6 to 1, he gave Iron Man a POWER FLUCTUATIONS complication. To drive home the point, I activated Iron Man's limits to shut down some powers at the same time. It made narrative sense and gave Electro a little respect from the players before they took him down.