Not that this has anything to do with online slots but heres an example of land based slots revenue for September 2005:
Foxwoods Casino:
Total Slots Handle = $804 million from 7439 slot machines (Thats $108079 per machine).
Total Slots Win = $68.8 million. ($8980 per machine).
Hold percentage = 8.3%
Mehegan Sun:
Total Slots Handle = $882.4 million from 6204 machines (Thats $142230 per machine).
Total Slots Win = $74.9 million ($12073 per machine).
Hold percentage = 8.49%
I just need two or three machines to make a good living.