Some more backwards incompatible changes (minor though), also a ton of small cleanup.

onPluginEnable(PluginEvent event)   -> onPluginEnable(PluginEnableEvent event)
onPluginDisable(PluginEvent event)  -> onPluginDisable(PluginDisableEvent event)
onVehicleUpdate(VehicleEvent event) -> onVehicleUpdate(VehicleUpdateEvent event)
onWorldSave(WorldEvent event)       -> onWorldSave(WorldSaveEvent event)
onWorldLoad(WorldEvent event)       -> onWorldLoad(WorldLoadEvent event)

src/main/java/org/bukkit/event/world/ChunkEvent.java

@@ -0,0 +1,21 @@
+package org.bukkit.event.world;
+
+import org.bukkit.Chunk;
+
+public class ChunkEvent extends WorldEvent {
+    protected Chunk chunk;
+
+    protected ChunkEvent(Type type, Chunk chunk) {
+        super(type, chunk.getWorld());
+        this.chunk = chunk;
+    }
+
+    /**
+     * Gets the chunk being loaded/unloaded
+     *
+     * @return Chunk that triggered this event
+     */
+    public Chunk getChunk() {
+        return chunk;
+    }
+}

src/main/java/org/bukkit/event/world/ChunkLoadEvent.java

@@ -6,21 +6,8 @@ import org.bukkit.Chunk;
 /**
  * Called when a chunk is loaded
  */
-public class ChunkLoadEvent extends WorldEvent {
-    private final Chunk chunk;
-
-    public ChunkLoadEvent(final Type type, final Chunk chunk) {
-        super(type, chunk.getWorld());
-
-        this.chunk = chunk;
-    }
-
-    /**
-     * Gets the chunk being loaded/unloaded
-     *
-     * @return Chunk that triggered this event
-     */
-    public Chunk getChunk() {
-        return chunk;
+public class ChunkLoadEvent extends ChunkEvent {
+    public ChunkLoadEvent(final Chunk chunk) {
+        super(Type.CHUNK_LOAD, chunk);
     }
 }

src/main/java/org/bukkit/event/world/ChunkUnloadEvent.java

@@ -7,11 +7,11 @@ import org.bukkit.event.Cancellable;
 /**
  * Called when a chunk is unloaded
  */
-public class ChunkUnloadEvent extends ChunkLoadEvent implements Cancellable {
+public class ChunkUnloadEvent extends ChunkEvent implements Cancellable {
     private boolean cancel = false;
 
-    public ChunkUnloadEvent(final Type type, final Chunk chunk) {
-        super(type, chunk);
+    public ChunkUnloadEvent(final Chunk chunk) {
+        super(Type.CHUNK_UNLOAD, chunk);
     }
 
     /**

src/main/java/org/bukkit/event/world/WorldListener.java

@@ -26,9 +26,9 @@ public class WorldListener implements Listener {
     /**
     * Called when a world is saved
     *
-    * param event Relevant event details
+    * @param event Relevant event details
     */
-    public void onWorldSave(WorldEvent event) {
+    public void onWorldSave(WorldSaveEvent event) {
     }
 
     /**
@@ -36,6 +36,6 @@ public class WorldListener implements Listener {
      *
      * @param event Relevant event details
      */
-    public void onWorldLoad(WorldEvent event) {
+    public void onWorldLoad(WorldLoadEvent event) {
     }
 }

src/main/java/org/bukkit/event/world/WorldLoadEvent.java

@@ -0,0 +1,9 @@
+package org.bukkit.event.world;
+
+import org.bukkit.World;
+
+public class WorldLoadEvent extends WorldEvent {
+    public WorldLoadEvent(World world) {
+        super(Type.WORLD_LOAD, world);
+    }
+}

src/main/java/org/bukkit/event/world/WorldSaveEvent.java

@@ -0,0 +1,9 @@
+package org.bukkit.event.world;
+
+import org.bukkit.World;
+
+public class WorldSaveEvent extends WorldEvent {
+    public WorldSaveEvent(World world) {
+        super(Type.WORLD_SAVE, world);
+    }
+}