Regarding Eye for an Eye, I agree with what Trixxy posted except on when to use the skill. Since the skill has a chance of debuffing the enemy with every hit the enemy makes, and a tank who's in the middle of a pull is doing their best to keep enough distance from the mob so they don't get hit, it's kind of a waste to use the skill in the middle of the pull. Instead, use it shortly after the tank's done pulling and is standing in place for DPS to attack. Furthermore, if your tank isn't the kind to get initial aggro on everything along the way (i.e. use skills as they run so every monster's name is in red, not orange), you would pull aggro from having used a skill on the tank.

A nice way to handle large pulls is to estimate where the tank is going to stop, Divine Seal + Medica 2 so that the spell will hit right after the tank's stopped moving and has initial aggro on everything (DS+Swiftcast+Med2 if needed), Regen, and then Eye for an Eye while your skills are on global cooldown.
This combo and maybe a Cure2 to top off the tank gives WHMs the best opportunity to throw out some Holy's because the healing-over-time from the regen effects is almost as big having a Cure casted every 3 seconds. Plus the Holy's keep stuff stunned for a few seconds, possibly interrupting some enemy skills, buying more time for the regens to do their work while you help the mob die faster so less healing needs to be done in the long run. (Even if you don't like to cast Holy, taking advantage of Med2+Regen makes mobs significantly easier to manage.)

After that, if the mob still isn't dead, the effects of Eye for an Eye can get pretty noticeable on very large mobs. Sometimes, you'll get parties where the mob is still alive after over a minute; it's mostly because of this that I suggest to use the skill after the tank's done pulling instead of using it at the start of a pull and losing 10+ seconds on it.