I think it is a great innovation that is good for the democratic nature of the web. Some quotes from the article in your second link that I liked:

1. With Opera Unite, we are giving developers a chance to develop applications (known as Opera Unite services) that directly link people’s personal computers together, so that you can connect with one or more of your friends at the same time. It all happens through the browser, so no additional software has to be downloaded, and it will work wherever Opera works (Windows, Mac, Linux, and later mobile phones and other devices). Opera provides the platform and you provide the applications—what you create is limited only by your imagination.
2. The key to Opera Unite is that it enables a whole new class of social software on the Web, applications that benefit from two or more people being online at the same time. And, with Opera Unite, these people can all connect directly without needing middlemen who control third-party servers.
3. Currently, most of us contribute content to the Web (for example by putting our personal information on social networking sites, uploading photos to Flickr, or maybe publishing blog posts), but we don’t contribute to its fabric — the underlying infrastructure that defines the online landscape that we inhabit.
4. Our computers are only dumb terminals connected to other computers (meaning servers) owned by other people — such as large corporations — who we depend upon to host our words, thoughts, and images. We depend on them to do it well and with our best interests at heart. We place our trust in these third parties, and we hope for the best, but as long as our own computers are not first class citizens on the Web, we are merely tenants, and hosting companies are the landlords of the Internet.
5. We are connected to a Web that has democratized much and is an amazing source of information. However, “the wisdom of the crowd,” along with the notion that our data ought to live on other people’s computers that we don’t control, has contributed to making the Internet more impersonal, anonymous, fragmented, and more about “the aggregate” than the individual. In fact, quite the opposite of the original promise.
   

My boldings.
Note the comment made by http://my.opera.com/cshmuch/about/

You can use XMLHttpRequest in your own service's code, and then call xhr.open("GET", "http://your.local.domain" + e.connection.request.uri, false); // it will work =)

Source: http://unite.opera.com/service/192/

Related WPW thread: Web browsers converging to net operating systems?

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