sundaridevi - 3:12 pm on May 3, 2011 (gmt 0)
Everybody is obviously working with different sets of information, knowledge and assumptions here, so without a baseline the discussion isn't very effective.
As far as Google products are concerned, they do, unquestionably affect search results. That means, in some cases, what you see, is different from what the guy sitting right next to you sees. You can test this, get a google account (mail, analytics, whatever), after you've had this account for awhile, log in and do some searches while you are logged in. If you note your results. Log off, launch another browser that you rarely use or that has all cookies removed and search again (or just close your browser, delete private info like cookies and relaunch). You will see different results (at least in very competitive categories). Previous searches also influence the adwords you will see (as long as cookies are not deleted). If I have the toolbar installed and am not logged into an account, I still see different results than if I am logged into an account.
Does geolocation affect search results? You bet, get a UK vpn and search. You will get different results than if you are located in the USA (e.g. have a US IP address). This is again, unquestionable. Google country-specific sites also give different results for the same user location. To test, search for something in Google.co.uk, or google.au and watch the results change.
Sure, that is Google improving our user experience. But this is not the same question as saying, what is the baseline search result. In other words, my objective is to have the best SERPs possible for the vanilla search (i.e. the user who has no google search history in his cookies, etc) in whatever location he chooses to be. It is not possible to control what Google decides is a better result based on what the guy looked for over the last week or where he is located (although you can optimize for country-specific sites - or for Places, which is outside the scope of this discussion).
This means as far as SEO is concerned, if you wish to set on-site factors aside, a user experience can only be based on the way the user interacts with the site (page views, time on site, frequency of return, etc), assuming google actually has the capacity to measure such factors.