I guess bitcoin gambling accounts for a significant portion of the bitcoin economy. It is tough to quantify this though. I remember reading that Satoshi Dice accounted for 25-50% of all bitcoin transactions last year. According to reports, the gambling industry is poised to grow further.
https://www.cryptocoinsnews.com/bitcoin-will-revolutionize-gambling/I think major sectors in the bitcoin economy would be
- Mining
- ASIC Manufacturing (Aren't these purchased primarily using bitcoins)
- Gambling
- Trading (Bitcoin exchanges)
- Bitcoin Mixing
- Remittance
- Pornography (Girls Gone Bitcoin, among others
)
- Illegal activities (Buying drugs, Ransomware, etc)
- Ancillary Services (Legal, Compliance, Bitcoin software, etc)