Mainly useful for watching models and re-rendering when they change.

Something like this:

var user = new EventEmitter();

React.createClass({
  render: funtion() {
    return <p>
      Name: <input type="text" name="name" value={user.name} onChange={this.handleChange} /><br />
      Email: <input type="text" name="email" vaue={user.email} onChange={this.handleChange} /><br />
      <Observe target={user} handler={function() {
        return <a href={'mailto:' + user.email}>{user.name}</a>
      }} />
    </p>
  },

  handleChange: function(e) {
    user[e.target.name] = e.target.value;
    user.emit('change');
  }
});