I would be willing to bet that the bulk of font piracy occurs at the corporate level. Many workgroups will actually be a licensed for a font family, but for far less users than actually use the software.
And that's not to say that it's malicious, either. Many workgroups just have a hard time keeping track of which fonts are licensed for how many users.
I'm sure their are also many individual font traders out there, but they are small potatoes compared with the big corporate abusers.