title: React slow with lots of textareas (but not text input fields)
body: <p>With lots of textareas, my (admittedly large) form becomes sluggish.</p>
  
  <p>With text input fields instead, however, everything is snappy.</p>
  
  <p>I've created two minimized testcases, one with textareas and one with input fields. Click the toggle button to show/hide a group to see the issue. With Chrome, at least, the group is really slow to toggle in the textarea version.</p>
  
  <p>2500 textareas:
  <a href="http://jsbin.com/wudujusoji/edit?html,js,output" rel="noreferrer">http://jsbin.com/wudujusoji/edit?html,js,output</a></p>
  
  <p>2500 text input fields:
  <a href="http://jsbin.com/rezudotojo/edit?html,js,output" rel="noreferrer">http://jsbin.com/rezudotojo/edit?html,js,output</a></p>
  
  <p>What am I doing wrong here? Shouldn't the textarea and text input field versions be roughly the same performance?</p>