Did you know that if you are logged into your Google account (such as Analytics, Reader, Adwords, Adsense, Igoogle etc), and you run checks on your rankings in Google, the positioning for various phrases can be different (usually better) than if you weren’t logged in. Quite an easy thing to miss, if even you are seasoned web professional!
The reason for this, is the Google personalised results feature – so if you are logged into your Google account and run searches, the search results will be personalised based on your prior search history.
Here’s a website that can turn off the personalisation.
See this post from Google for more information about personalised results.