Many employees in newly Holacracy-powered companies experience a period of being uncomfortable not having a boss. They aren't used to dealing with the responsibility of having so much autonomy. Although, with time, most people get the hang of it and become more responsible individuals capable of handling the authority they have in the roles they fill for the company. (I just read the Holacracy book.)
There aren't any informal hierarchies. It's a very structured system, just a different structure than the traditional hierarchical management system. (I just read the Holacracy book.)