Disable potion particles. Works in Minecraft 1.7.2 - 1.5.2.

DisablePotionParticles.java

package com.comphenix.example;

import java.util.List;
import org.bukkit.entity.Entity;
import org.bukkit.plugin.java.JavaPlugin;

import com.comphenix.protocol.PacketType;
import com.comphenix.protocol.ProtocolLibrary;
import com.comphenix.protocol.ProtocolManager;
import com.comphenix.protocol.events.PacketAdapter;
import com.comphenix.protocol.events.PacketEvent;
import com.comphenix.protocol.utility.MinecraftVersion;
import com.comphenix.protocol.wrappers.WrappedWatchableObject;

public class ExampleMod extends JavaPlugin {
    private static final MinecraftVersion POTION_CHANGE = new MinecraftVersion("1.6.0");
    
    @Override
    public void onEnable() {
        final ProtocolManager manager = ProtocolLibrary.getProtocolManager();
        final int POTION_INDEX = manager.getMinecraftVersion().compareTo(POTION_CHANGE) <= 0 ? 8 : 7;
        
        manager.addPacketListener(
          new PacketAdapter(this, PacketType.Play.Server.ENTITY_METADATA) {
            @Override
            public void onPacketSending(PacketEvent event) {
                Entity entity = event.getPacket().getEntityModifier(event).read(0);
                
                // Disable "personal" potion effect particles.
                if (event.getPlayer().equals(entity)) {
                    modifyWatchable(event, POTION_INDEX, (int) 0);
                }
                
                // You can also disable potion effects on other player entities too.
            }
        });
    }
    
    /**
     * Set the value of a particular watchable object, if if is present in the list.
     * @param event - the packet event.
     * @param index - index of the watchable object.
     * @param value - the new value, if the object is present.
     */
    private void modifyWatchable(PacketEvent event, int index, Object value) {
        // Determine if we need to modify this packet
        if (hasIndex(getWatchable(event), index)) {
            // We do - clone it first, as it might have been broadcasted
            event.setPacket(event.getPacket().deepClone());
            
            for (WrappedWatchableObject object : getWatchable(event)) {
                if (object.getIndex() == index) {
                    object.setValue(value);
                }
            }
        }
    }
    
    /**
     * Fetch the current list of watchable objects.
     * @param event - the packet event.
     * @return List of watchabel objects.
     */
    private List<WrappedWatchableObject> getWatchable(PacketEvent event) {
        return event.getPacket().getWatchableCollectionModifier().read(0);
    }
    
    /**
     * Determine if a watchable object is present with the given index.
     * @param list - the list of objects.
     * @param index - the index.
     * @return TRUE if there is such an object in the list, FALSE otherwise.
     */
    private boolean hasIndex(List<WrappedWatchableObject> list, int index) {
        for (WrappedWatchableObject object : list) {
            if (object.getIndex() == index) {
                return true;
            }
        }
        return false;
    }
}

Note: that class don't remove potion particles, it makes them only more transparent ("ambient") but you can see them anyway