The most common use case was users hooking it up to a cheap netbook plugged in to a HDTV in the office or displayed on a 2nd monitor. In this case most small companies would use 2 devices max, a machine to configure and another to display. Perhaps unsurprisingly larger companies used it on more HDTVs (some use upward of a dozen) but they would rarely have more than one dashboard.
However, there are certainly a number of different use cases. Solo users, SMEs, large enterprises and agencies all have different usage patterns and finding a one-size-fits-all is almost impossible. I evaluated 'per device' to be the least bad option based on the data at my disposal. That said, it's early days and there are no sacred cows here, I'm always open to suggestions.