title: CSS3 PIE: rounded corners slow down IE9, even though it supports them natively
body: <p>I'm using <a href="http://css3pie.com" rel="nofollow">CSS3 PIE</a> to add support for rounded corners to IE7/8. I've found that when I have lots of elements on the page with rounded corners, performance in <em>IE9</em> drops considerably when PIE is enabled: scrolling becomes laggy, simple hover effects (like link color changes) become significantly delayed, etc.</p>
  
  <p>But according to PIE's own documentation, PIE "does nothing" in IE9 if the browser natively supports the particular CSS3 feature you're using. Theoretically, then, if I'm only using border-radius (which IE9 supports), enabling PIE should have no effect on performance.</p>
  
  <p>What could be causing this?</p>