Bashiok posted today a sneak peek into the upcoming 4.0.1 patch changes for the Death Knight, Druid, Hunter, Warrior, Paladin and Warlock classes. (source)

Blizzard Quote:

Patch 4.0.1 will bring about major changes to all World of Warcraft classes, including sweeping talent tree revamps, altered spells, and improved abilities. We wanted to go over some of the more complex changes that are being made. If your class isn’t listed here, it does not mean we didn’t spend as much time on it — the class will still receive a broad range of updates to talents, spells, and abilities — we simply feel that these mechanics merit additional explanation.

Death Knights

Runes

  • The way in which runes regenerate has been changed. Rather than each rune type (Blood, Frost, Unholy) regenerating simultaneously, they now fill sequentially. For example, if you use two Blood runes, then the first rune will fill up before the second one starts to fill up. You essentially have three sets of runes filling every 10 seconds instead of six individual runes filling every 10 seconds. This allows the death knight rotation to be more forgiving, so that the player can take advantage of things like ability procs or respond to movement. This system makes it a little easier to get back on track without six separate runes now “out of sync” from the standard rotation.

You’re a Bloody Tank

  • The time has come to dedicate a death knight talent tree to tanking, and that is what is in store for the Blood tree. We felt that we could offer a more focused and polished tanking tree rather than having to scatter similar tools throughout the trees. This also allows us to really focus the other trees into more flavorful damage-dealing specializations.

Runic Empowerment

  • This mechanic allows for runes which were on cooldown to instantly activate, which prevents the rotation from becoming too predictable and boring.

Druids

    Eclipse

    • This is a new mechanic being added for Balance druids. The resource is managed through a new bar near the health and mana bars. As the druid casts Arcane spells, the bar moves towards the sun element until the druid achieves a Solar Eclipse, which buffs Nature damage. The goal is then to cast Nature spells, until the bar moves toward the moon element, which triggers a Lunar Eclipse and buffs Arcane damage. The gameplay becomes trying to quickly move the bar from one end to the other in order to maximize each Eclipse buff.

Hunters

    Focus

    • This is a new resource which has replaced mana. Hunters never felt like they should be casting mana-based spells, and having a resource that lasted for a long time and then was painfully gone didn’t lead to compelling gameplay.

    Pets

    • Hunters can now use Call Pet to choose from among five different pets. They can swap out any of these five pets with other pets they have tamed by visiting a Stable Master. The Stable Master now allows the hunter to store twenty pets total.

    • Pet families have been updated. Each family can now provide unique buffs to parties or raids, so if a class buff is needed for a raid and that class isn’t represented in the group, chances are a hunter can provide a little assistance by calling out a specific pet.

    Ammo

    • Ammo is no more. As a hunter, you’re just that good now.

    • Any quivers or pouches used to store ammo will automatically be converted into a bag of roughly equal value.

Paladins

    Holy Power

    • This is a new resource which works similarly to combo points. Paladins will generally want to build up Holy Power until it shines through with a bright yellow glowing effect. Once Holy Power has been built up, it can be consumed to augment existing abilities. For example, Word of Glory can be used to cast an instant-cast free heal. This gives paladins several options for how to spend their Holy Power, depending on the scenario.

Warlocks

    Soul Shards

    • As items, Soul Shards are going away entirely.

    • Any shard bags used to store Soul Shards will automatically be converted into a bag of roughly equal value.

    • Soul Shards are now a new resource for warlocks. Each warlock will have a total of three. These Soul Shards can be expended using a new spell, Soul Burn, which allows the warlock to augment the next spell cast. The augmentation effect will vary depending on which spell is used, and all warlock spells which can be empowered by Soul Burn will have a tooltip listing of the effect it grants. Soul Shards will no longer be necessary for summoning demons or casting any other spell typically used when out of combat.

Warriors

    Rage

    • Rage is being normalized so that its generation is no longer based on damage done by auto-attacks. Each auto-attack will provide a set amount of Rage, with off-hand weapons granting 50% of the rage main-hand weapons do. Haste will allow Rage to generate more rapidly by increasing attack speed. In addition, while taking damage, the amount of Rage generated will now be based on the warrior’s health rather than the opponent’s level. The essence of this change is to improve the scaling that occurs with warrior gear. With warriors balanced around the top tiers of items, we’ve found that the class tends to underperform more drastically than others in lower-quality items. These changes should correct that.