At the risk of being pedantic, I want to question the equivalence Chris sets up between being a manager and being a boss. He may just mean the same thing by the two terms, but there is a distinction in principle. An enterprise that was wholly owned by its workers, and in which all major planning, investment and directional decisions were taken through democratic structures and procedures, would still have need for day-to-day management in the sense of coordination, assuming it was of a certain size. No large outfit can run efficiently if the different parts of it aren't working in ways that harmonize with one another, and if it were to do everything - every detailed thing - by way of a meeting of the entire membership its processes would be cumbersome. So, though it had no bosses, it would need people to carry out this coordinating function, even if the function rotated from one person to another at regular intervals. While they were responsible for that function, such people might be called managers.
See the following passage from chapter 13 of volume 1 of Capital:
[W]hen considering the capitalist mode of production, he [the political economist]... treats the work of control made necessary by the co-operative character of the labour-process as identical with the different work of control, necessitated by the capitalist character of that process and the antagonism of interests between capitalist and labourer.See also chapter 23 of volume 3 - the long passage that begins with the analogy of the 'orchestra conductor'.