I hardly ever use it. I have tried setting up various macros but find it very hard to use. Here us my current one:
#showtooltip
/cast [target=focus,raid,nodead,nomodifier:ctrl] Intervene; [raid] Intervene; [target=targettarget,raid] Intervene
I've set up my focus target to be the healer but it doesn't always work that well... When pitbull lights up a party member in red (suggesting that they have aggro) I mouse click that player, then hit my keyboard shortcut for Intervene (though if its the focus target I just Ctrl-click the hotkey without selecting him first of course). 50% of the time the party member turns out to be too close, the other 50% it works. Not exactly ideal...
I've thought of setting up a macro for each party member next to their health bar (similar to having a focus target so I don't have to select the part member first), but not sure... So far I can regain aggro more consistently using taunt, mocking blow, or challenging shout.
You guys use it actively? How?