There is so much to cover that it's a little overwhelming. Over the next week we will be covering all the changes in more detail, but for now I would like to address a few changes that seem to be the same for most classes. For example, almost every Heal over Time (HoT) or Damage over Time (DoT) will now be effected by Haste through the addition of ticks rather than just ticking faster. This is a huge change for almost every class.
Currently Haste can affect some DoTs so they just run their course of damage faster, making Shadow Ward: Pain, for example, do the same amount of damage in less time. In Cataclysm, Shadow Ward: Pain will stay up for it's normal duration, 18 seconds in this case, but do more damage because your Haste has added more ticks in the 18 seconds it's up.
This change is, in my mind, the perfect use of Haste for casters' HoTs and DoTs because it's simple and it's a good way to control how much damage is being output. Under the Warlock changes, Blizzard says something very interesting, "When reapplying a DoT, you can no longer "clip" the final tick. Instead, this will just add duration to the spell, similar to how Everlasting Affliction currently works."If this change will affect all Hot's and Dot's, the play style of many players will have to change. You will no longer have people spamming keys to get the HoT or DoT back up. What you will have is a much more relaxed single pressing of a key to add time to the spell.