Google is now rolling out its personalised search feature to all visitors, including those who are not logged in to a google account. Personalised search means that your search results in google are influenced by what you have already clicked on in the past. Previously, google account holders used their web history to show personalised search results, but now google are using a secure cookie based system to guess what sort of results you are likely to click on. There is the option of turning this off, but for the majority of non techie visitors, this will not be used, so the assumption will be that most people will have personalised search turned on.

What this means for SEO is that you need to make sure your site can be easily found, and that people will want to repeatedly click on your links. This means having good metatags and titles that are descriptive and representative of the content, and by having good content behind it.

What this also means is that we could start seeing 'rotating serp spamming' whereby grey hat SEO companies use regularly updated misleading text to entice people to click on their results, and thus push them up the rankings, then change the metatags and titles so that the next time people see the result in their serps, they click on it again, not recognising that it is a spammy or irrelvent site that they have already visited. This will then further push the link up the rankings ready for another metatag revision.

Heres a video from google that explains more how personalised search works: