Opera hopes to change the way we use the web with Opera Unite. "We promised Opera Unite would reinvent the Web," said Jon von Tetzchner, Opera's CEO, "What we are really doing is reinventing how we as consumers interact with the Web. By giving our devices the ability to serve content, we become equal citizens on the Web. In an age where we have ceded control of our personal data to third-parties, Opera Unite gives us the freedom to choose how we will share the data that belongs to us."
Opera's website gives a decent short introduction to Opera Unite, and what, exactly, you can currently do with it.
This is just the beginning, though, as developers can build applications that make use of Opera Unite to do all sorts of things. Data shared via Opera Unite can be accessed via other browsers too, but some applications may be designed specifically around Opera-Opera interaction.
You can download Opera 10.10 for your platform of choice straight away.