Time crediting. You are only paid for the hours that you are logged into the computer, and if you want to take a break there's a 30 minute minimum before the program will let you log back in.
Performance-based compensation. Afaik, everyone starts at a flat $7.30 an hour, and /all/ additional pay raises are contingent upon your performance as measured by the speed with which you complete jobs. Furthermore, these pay raises are calculated on a pay period to pay period basis. This means that if you do exceptionally well for two weeks then kinda fall flat, you will only get the bonus pay for the two weeks you did well.
Scheduling woes. You can always move hours forward, but backward requires either one week+ notice, a really good reason, or adding extra hours. This issue can be exacerbated if there's a larger than average amount of jobs floating around in the system. Also, there is a 16 hour a week scheduled minimum, and Saturdays and Sundays don't count towards this.
Adversarial client/customer relationship. Clients are charged based on how long they take to dictate their message, and scribes are paid based on how quickly they transcribe a message. Clients want to make their message as short and dense as possible, while scribes would be better served by longer and less dense messages.