Yup, works perfectly here too, it's brilliant.
So long as you STOP the video on one device, you can play back that video back on another, immediately. Watched status is also synchronised immediately, too, when working correctly.
I would enable DEBUG mode, then check the log to ensure that all machines are actually pointing at the SQL database - I wonder if it is failing to connect, and falling back to the local library?? (If you make sure you delete the local library, then you'll instantly see that there is no media if this is happening. If you've still got a local library pointing at the same sources, you may not notice whether it's using the local or centralised database)