It's common knowledge that Google knows what you're up to.  One of the things it knows about is what you've searched for - a history of everything you've looked for on your browser - well, maybe not everything, maybe just the things you search for a lot. 

So, for example you might be an SEO who likes to check that he's top of the pile of all the SEO's in Anytown.  What's he going to search for?  Something like SEO Consultant Anytown, perhaps?  The thing is, he's going to do that search probably every month, maybe every week, maybe even every day.  Google knows he frequently visits his site, www.seoconsultantanytown.co.uk, and so Google shows his site pretty high up the SERPS for his frequently entered search term.

All that can be got around by going "In Private" (activated in Internet Explorer and Firefox by the keystrokes Ctrl + Shift + P).  This hides any history that Google, or any other search engine may have left lying around on your PC in the form of a cookie.  Great.  Now our SEO guy can do his search without fear of Google favouritising (I don't know if that's a word!) his site.  He then finds he's not ranking at position 1, he's on page 2.  Back to the on page and link building drawing board then...

In a few months time our SEO maestro has now achieved position 1 in Google (using In Private mode) for his favourite search term.  At least he thinks he is.  Over at SEO Chaps Ltd, they're ranking number 1 for SEO Consultant Anytown too.  And they're using In Private, so no danger of cookies.  What's going on?

Our SEO maestro is now at an SEO convention in Anytown.  He's so confident when he's doing his presentation that he shows the audience how good he is at SEO.  He uses his favourite search phrase... and he's number 5.  Not number 1.  Devastated, he heads to the local pub for a beer and accesses his site on his iPhone, via the pub's wifi. Number 5 again.  Back at his office he's number 1.

Could Google be doing this? It certainly is possible - and makes a lot of sense too.

By the way, this story isn't based on a true story, but it might just happen one day very soon....