http://wow.curse.com/downloads/details/12837/

This addon updates the health of player/party/raid members and pets much faster then normal by using the combat log rather then waiting for the server to send updated health info.

It works with blizzards default UI as well as ANY custom addon you might have installed. All you need to do is put it in your addons folder and enable it!
Notice, this addon only speeds up health updates for player/party/raid members and pets. Players/mobs that's not in your group will have their health updated like normal. This due to the fact their exact health is not know to the client which is needed for the addon to calculate someones health.

There is one know issue with this addon, damage meters seems to be unable to register effective healing properly for those having this addon installed. This is likely to be due to there being no delay between someone getting a heal and their health being updated, so the damage meter thinks it's overhealing.

Here are some details for the interested reader:
The server doesn't send health updates faster then once every 0.3 seconds, sometimes it's slower.
Combat log messages are sent as soon as the event happens making damage and healing show at the client before the affected units health is updated.
There are strong indications that the server not just sends health updates a bit slow, but that it in fact calculates the health at intervals of roughly 0.3 seconds.
It is possible, sometimes, to get in a heal on someone with negative health if the heal lands almost exactly after the health drops to negative. If it's a instant cast heal and it's cast to slow but before the client knows the target is dead the heal is wasted and the person still dies.
This addon in itself uses very little system resources (up to around 100 kb of memory in 25 man raids), it does however make all unit frames and other addons listening for the HEALTH_UPDATE event to do more work, but if wow runs fine with the addons you have installed already you shouldn't notice any difference running this addon as well.

so, in short, it works with grid? sweetness.

yep! and it finally explains all those "my heal went off but the tank died" moments. at least we finally know we weren't being ripped off, the tank was already dead, your client just didn't know yet. :(

It was a crit too =(

[Kimbelin] [Bullshit] crit [You] 9999
[You] die.

I don't see how this does anything to affect heals going off on your screen but not actually landing. That will still happen. And they will crit. We always knew what was actually going on behind the scenes. This isn't news imo.

Well, you'll see them dead as soon as they really die, not 0.3 seconds later. How that interacts with the client I do not know. For example, does the updated "dead" status from this mod cause the spell to fizzle on the client side with a "your target is dead" error? Or is this purely graphical?

I'm assuming it's purely graphical. Also, you don't know the tank is dead as soon as they really die, just the delay is your latency rather than your latency + 0-.3 seconds, so you'll still have heals go off that don't land, even graphically.