CountUpDown + Safari's Web Clip button = instant Dashboard countdown widget.

The web clipping above is generated like this:

<div class="web-clip-container">
  <iframe class="web-clip" src="http://countupdown.appspot.com/Apple_WWDC_Keynote_2008">
  </iframe>
</div>

<style type="text/css">
.web-clip-container{
  height: 550px;
  margin-bottom: -120px;
}
.web-clip{
  height: 550px;
  width: 100%;
  border: none;
  scroll: none;
  position: absolute;
  left: -130px;
  clip: rect(20px, 550px, 420px, 160px);
}
</style>