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Plume (free and paid version)
I am a heavy Twitter user and Plume is my preferred method to interact with the social network on the Nexus 7.
The app displays a single column timeline in portrait, but when you rotate into landscape it presents three columns of the user's choosing.
Flipboard only recently was released for Android, and it is great to use on the Nexus 7.
Keep up with news and your social networks in one interface that looks spectacular on the Nexus 7 screen.
I confess I use Google + far more now that I have this app on the Nexus 7 than I ever did before.
It presents the updates from the people I follow in an outstanding graphical way that works fluidly on the Nexus 7.