Eg a mobile client app ought to be storing enough data on the device that I can read my notifications and timelines offline. Obviously I would only see posts up to the last time the device was connected to the net, and recall of older posts would be limited by a sane storage limit. I'd also like to be able to post of reply while offline, and have those posts sent the next time I connect. The UX would need some thought, but surely it's possible for apps to be used offline without freaking out.