Limitations of the Google OS
The Google OS probably has features like Amazon's S3 for distributed storage, distributed cpu features and all that.
But at the same time, to make that distributed stuff work, they must have sacrificed certain features that regular developers take for granted.
I ran into this problem when creating a distributed architecture for mefeedia. It's an aggregator, so the thing has to scale. Classic database approaches stop working beyond a certain point. So you need a distributed architecture.
But building that architecture comes with limitations compared with a classic relational database - I can no longer sort my entries by any field, like I could in a database, for example.
You can see similar limitations in Gmail. For example, you can't get a view of all your unread messages (did I miss it?). I don't believe this is because the Google engineers believe it's not an important feature, I think it's because they're limited by the Google OS.
The GoogleReader has similar problems.
In a message from the engineers, they explain why you can't just "mark all items as read": "Architectural limitations prevent us from offering these features immediately, but rest assured that we are investigating our options."
In other words, the GoogleOS datastructure let us scale large easily, but it's stopping us from doing certain things that you might expect to be easy.
The tradeoff is worth it, of course, and I'm sure the GoogleOS will incorporate more and more features and workarounds as it gets used by more Google products.