In 2013, the digital anthropologist Lui Smyth conducted a survey of the most common uses of bitcoin.
He found bitcoin was used to buy web services, software, hardware, gambling services, and (in the heyday of the Silk Road) narcotics. Topping the list though, when measured in terms of the number of transactions, was tipping and donations.
The public block chain provides much anecdotal evidence for this. All one needs to do is search the tipping addresses of people or groups who openly advertise that they take bitcoin tips.