For a while now, I've taken damage merely from people beginning their attack/charge animation. This occurs even if it's an attack that takes a while to charge, like a wolver's, or an attack that would move the enemy, like a jelly's. If I am next to the enemy when they begin animations, I get damage. This damage shows up even before the enemy completes their attack, so this is not a server ping/distance issue where I'm simply reacting too slowly.
If it helps, I'm using:
Windows 7 Ultimate (SP1) 64-bit
Intel i7 1.6 GHz CPU, overclockable to 2.5 GHz
4 GB RAM
Java 6.26
Its still lag though. Monster hits are managed on the server side and damage comes in at a slightly higher priority in the data stream then most positional data. With that in mind, you need to adjust for a certain amount of delay in movements if your kiting too close to a monster. Shields are different due to the fact it needs server feedback, so the effects tend to be more in sync with everything else going on.