What does not count: news reading, watching videos (even if educational), social networking, web browsing and email.
Why not? I set my tablet on the console for my stationary bike and keep up with TR and /. et al while I am working out. It allows me to legitimately do two activities in parallel that I would have done serially in the past. That sounds like the definition of productivity to me.
As others have noted, I use mine for PDF reference a lot. Working on the car, electronics, airplanes, anything where I need a ready reference. It saves me printing stuff and is much less cumbersome than a laptop. My tablet has actually replaced my work laptop too. A bluetooth keyboard and Citrix are all I need to be able to work remotely in a pinch. Its not the same as a full blown laptop of course, but it is much easier to carry around.