Basic questions:

1. Where is the data stored? How much redundancy? Obviously you need data to serve content.
2. How do you ensure that users are actually serving the correct data?
3. How will you validate the amount of data being served? (Imagine that an attacker controls both sending and receiving nodes. It would be trivial to fake the amount of bandwidth "used").
4. What types of data will you disallow? (This has many important legal consequences, as I'm sure you can imagine.) If everything is "allowed", I'd imagine most users unwilling to participate in fear of lawsuits/retaliation/subpoenas.
5. What is a "coin"? (unit of storage/bandwidth?) What is "difficulty"?