<p>Jeff answered a <a href="http://meta.stackexchange.com/questions/84695/eeeeek-where-is-my-slow-performance/84701#84701">question</a> over at M.SO in relation to why the SE network of sites are <em>so fast</em>.</p>

<p>The answer you are looking for (note that this doesn't mention SF, just "us", so I'm presuming all the sites.):</p>

<blockquote>
  <p>Google's crawler is now indexing us at, and I am not making this up,
  <strong>10 requests per second</strong>, which is the maximum.</p>
</blockquote>

<p>Lots of quick, topical, regularly updating content is working in SE's favour.</p>