The Google.com does not rank #1 for Google thread in our Search Engine Watch Forums looks at how Google has recently been returning not the URL of its own home page first in response to a search on Google but instead a redirected URL. In other words, rather than getting:
You sometimes get this URL ranked first in a search for google.
That looks like Google Desktop is being top ranked -- but note the https prefix. Rather than this being the Google Desktop site at http://desktop.google.com, it's instead a secure server that redirects to Google.
This has been an off-and-on situation from at least the beginning of this month, when the thread began. Google Blogoscoped noted the return of it happening again yesterday. Today, we seem back to "normal." Meanwhile, see the second comment at Google Blogoscoped in response to its story. It's a nice explanation of how this confusion is apparently caused by how SSL requests are treated if a certificate is declined.