The danger with online personalised news services is that they could become our sole window to the world.
The concept of personalised news isn't really new -- every news source is personalised by the editors and reporters who produce it. Most people tend to gravitate towards news sources which cater to both their interests and their bias. You can certainly see the different political leanings in Australia's major newspapers and radio stations. Sometimes the bias is less subtle than others, but even so if you read a major newspaper from cover to cover you'll still get a reasonably broad view of what's happening in the world.