Micro-gambling
Peer-2-peer gambling
Webcams
The real wonder is why haven't any of the major players in these areas adopted it in any way. Curiously it is the payment provider industry who has paid it some attention, rather than any of these.
Perhaps the traceable nature of bitcoin makes it unappealing for these use cases. In the early days of bitcoin where it was relatively easy to get anonymous bitcoins (by paying cash through unscrupulous dealers not paying attention to KYC rules), these would have made great use cases for bitcoin.
Now however, I feel like bitcoin doesn't provide relative anonymity over more traditional methods of payment.
I think there could still be a case for a new mail-like protocol that combines email and cryptocurrency for an email system which is both encrypted by default but also everyone sets a payment level for mail to reach them.
So I say "My Address is , pay at least 0.001 bitcoins to get mail through".
This system:
*Puts a direct cost on spam (therefore massively reducing it)
*ensures everyone owns private keys (so mail can be encrypted simply by knowing their address)
Two fantastic features.
Sadly it won't happen, mail is too entrenched.