Google tries to help with those sorts of search sessions. For 0.3% of queries, if we see a search for a query A and then another search for query B, and there appear to be good results related to both A and B, then we may surface those results.
For example, I just did the search [iphone] and then the search [wikipedia]. In addition to the regular results for Wikipedia, Google also surfaces the page http://en.wikipedia.org/wiki/IPhone . A good way to see that Google is doing this is to look for a phrase like "You recently searched for iphone" under the newly-surfaced results. Go ahead and try it with the search [twilight] and then the search [wikipedia] for example.
Between Gabriel's article and the WSJ article, words that are reported to provide this behavior include iphone, nexus, obama (but not romney, because there wasn't enough information for this word at the time the data was generated), tablet, twilight, computer, health, speech, iraq, sports, social security, and stock.
Just to reiterate, this algorithm affects 0.3% of searches on Google. Most Hacker News readers are savvy enough to search for [iphone wikipedia] instead of breaking that search into multiple queries. However, if you don't want Google to surface additional results that might help with your current query, Google has a support page telling how to turn off search history personalization: https://support.google.com/accounts/bin/answer.py?hl=en&...
As an aside, I wrote a blog post ~4 years ago to preemptively debunk the idea that Google skews our search results for political reasons: http://www.mattcutts.com/blog/google-search-and-politics/ We simply don't do that.
We used to have a problem with spelling where some news event would make a person with an uncommon name famous, but google would mistakenly correct it to a more common but incorrect name just because the spelling system hadn't ever seen this person's name before. We've fixed that issue and many other freshness related things: http://googleblog.blogspot.com/2011/11/giving-you-fresher-mo... but this is an ongoing area of focus throughout a lot of our systems.
It's an interesting problem because for many things recomputing the data faster will only fix a handful of queries, so from a raw impact standpoint hardly seems worth it. However those queries end up being ones that are in the news and related to things that people care a lot about.
So pretty please: http://vanilla.google.com . Just like the old days :)
> obvious and opt-out
I'd tell you to pick one, but that implies choice. You can only pick google.