React 0.13 allows you to use ES6 classes. Feels so funny to be writing `super` in JavaScript, but it's really a nice and clean componnent.

rightDropZone.js

import React from 'react/addons';
import { DonorCard } from './donorCard.js';

export class DropZone extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      draggedOver: false
    }
  }
  render() {
    let classList = 'drop-zone ' + (this.state.draggedOver ? 'dragged-over' : '');
    return (
      <section
        className={classList}
        id={this.props.id}
        // http://facebook.github.io/react/blog/#autobinding
        onDragOver={this.handleDragOver.bind(this)}
        onDragLeave={this.handleDragLeave.bind(this)}
      >
        <p>Drop Zone</p>
        <DonorCard draggable="true" header="Ivan Storck" body="One Million DOLLARS!!!" />
      </section>
    );
  }
  handleDragOver(ev) {
    ev.preventDefault();
    this.setState({draggedOver: true})
  }
  handleDragLeave(ev) {
    this.setState({draggedOver: false})
  }
}