Bill Slawski, over at Cre8asite Forums, tears deep inside how Google Suggest suggests terms for you, as you type them. Of course, we have the Google Suggest FAQ but that doesn't explain it how Bill does.
Bill believes that the terms suggested come from the following four criteria; - Most Popular Searches - Hot News Topics - Recent Search Activity - Most Used Cache Query
However, Bill then goes through the process of how he located and examined this new Google patent application named Anticipated query generation and processing in a search engine. Based on his finding and tests in that document, Bill concludes;
This very quick, and very rough search shows Google returning queries which are likely the most popular in terms of people searching for them, and in the instance of ryanair, a word that is very topical right now.
He also greatly expands on this at his blog entry he titled; Can Google Read Your Mind? Processing Predictive Queries.
Forum discussion at Cre8asite Forums.