From Infothought:

1. Google query syntax underwent some subtle changes over the years.
Not too long ago, you couldn't enter more than 10 words into the Google search box. Or to be more precisely, you *could*, but subsequent words were ignored. I bet the Google founders were thinking "10 words ought to be enough for everyone," and mostly there were right – but for some advanced uses, especially with the Google Search API, a little more is helpful. Then, a while ago, Google increased the words limit to 32 words. This is probably OK for a few more years!

Another change is that Google ignores stop words nowadays. Stop words in search engines are words like "the" or "a" which are too tiny or common to be useful additions to most searches. However, Google is now accepting them as semi-normal words (one remaining difference being that they're not highlighted, or linked to the dictionary). This means in Google.com, you get different results when search for [the tale of a cowboy] vs [* tale * * cowboy] vs [tale cowboy]. (I'll be using square brackets around search queries – they're not to be included in the search.)

Another operator changed its functionality during the years; a couple of years ago, you could only query Google for [site:something.com], but not [site:something.com/something/]. Today, you can add folders to the site operator.