I'm not able to enable offline drive in either the new or old Drive interface.
In the new interface, I select "Offline" > "Sync..." > "Done", and when I open the dialogue again, my settings have have not changed.
In the old interface, I select "Enable Offline" and the page never completes loading, and I get stuck in an endless loop of network requests to:
https://docs.google.com/static/doclist/client/js/2418050222-offline_launcher_i18n_offline_launcher_core.js
304 response
https://docs.google.com/offline/optin?json=1
400 error
Screencast gif here: https://dl.dropboxusercontent.com/u/126030141/Share/offline-drive.gif