Opera Unite is not as decentralized as you may think. It still requires that you initialize connections via the machinename.username.operaunite.com domain that you are required to register with Opera. Sure, this is set up to easily traverse a NAT, but it isnt as decentralized as advertised (and you're restricted from hosting content that they consider "obscene, vulgar, hateful, threatening, or that violates any laws".
A more thoughtful take on the subject can be found here: http://factoryjoe.com/blog/2009/06/16/thoughts-on-opera-unite/
I honestly don't think Apple will care much. It leads to more people buying things from iTunes after all and cements the dominance of iTunes for managing media. Perhaps they even did this in conjuction with Palm... if you think about it they would have been smart to do so.
Think of iTunes as a driving force between iPod sales rather than the iPod as a driving force behind iTunes sales and you'll understand why Apple may be against this.
"One lawyer can steal more than a hundred men with guns." -- The Godfather