It is all too easy to create a Google account to gain access to all the free Google tools such as Analytics, Places, Merchant Center, AdWords (well, OK that one’s not really free) etc. and forget that you’ve ticked the stay signed in option.
If you select the “Remember web history” option in your Google account then Google will remember your browsing and deliver personalised results. It is easy to be lulled into a false sense of security that your site is ranking well, when in reality you might be seeing biased results.
Always remember to logout before checking your site ranking for Search Engine Optimisation OR add the parameter &pws=0 onto the end of the Google search string.