not sure if its a great idea from google. I think it would be good if you could just enable it to your account if you wish.
it only presents itself when you are logged into your google account so how can it affect the results?
Exactly - I cannot believe all the fuss about this. Does anyone read what Google says or did anyone watch the official release video? You have to be logged in to your account to have this feature. It must be a small fraction of users that even know how to log in to their account. Besides - IMO - most revenue from search comes from NOVICE search. Anyone that knows how to log in to their Google account is sophisticated enough so that he/she is a difficult candidate for revenue anyway.
The changes are only visible by you so there is no actual change in the global search results. It is only if you like something that is on the 2nd page (for example) and want to find it easy later. I find it to be a nice feature.