I'm using an implementation of Google's search API to create a daily automated ranking report. To my knowledge, no cookies are exchanged in the process, but the queries are fired off in quick succession from the same server each day.
The majority of queries includes a particular topic and a location qualifier, e.g. elbonian guesthouses, resorts in elbonia, and so on. The homepage of the particular website I'm checking this for usually ranks in the top 10 for these types of queries.
A minority of queries include either the location or the topic. Historically, the page is often displayed among the top 50, with a bit of yoyo-ing ...
Ever since Google announced that it would return personalized search results to its visitors who are not logged in, I've noticed the latter type of queries to return much higher rankings (top 10) for that site.
Am I paranoid to think that Google returns a skewed set of results for this particular sequence of queries, based on previous searches made by the same ip address either within the same session or over a period of time?