P2P projects have structure and hierarchies, but they are flexible. They are not structureless or hierarchy-less.
Below is a classic text on the topic.
Feminist and civic action groups of the sixties and seventies ... discovered that structureless anti-authoritarian modes actually lead to hidden power distributions, so that it is important to have open and transparent procedures that can insure a flexible and wide distribution of power. The following comes from a seminal essay on the subject:
Source: 'The Tyranny of Structurelessness', by Jo Freeman, Berkeley Journal of Sociology, 1970
"Contrary to what we would like to believe, there is no such thing as a 'structureless' group. Any group of people of whatever nature coming together for any length of time, for any purpose, will inevitably structure itself in some fashion. The structure may be flexible, it may vary over time, it may evenly or unevenly distribute tasks, power and resources over the members of the group. But it will be formed regardless of the abilities, personalities and intentions of the people involved. The very fact that we are individuals with different talents, predispositions and backgrounds makes this inevitable. Only if we refused to relate or interact on any basis whatsoever could we approximate 'structurelessness' and that is not the nature of a human group.
1. Delegation_ of specific authority to specific individuals for specific tasks by democratic procedures. Letting people assume jobs or tasks by default only means they are not dependably done. If people are selected to do a task, preferably after expressing an interest or willingness to do it, they have made a commitment which cannot easily be ignored.
2. Requiring all those to whom authority has been delegated to be _responsible_ to all those who selected them. This is how the group has control over people in positions of authority. Individuals may exercise power, but it is the group that has the ultimate say over how the power is exercised.
3 _Distribution_ of authority among as many people as is reasonably possible. This prevents monopoly of power and requires those in positions of authority to consult with many others in the process of exercising it. It also gives many people an opportunity to have responsibility for specific tasks and thereby to learn specific skills.
4. Rotation_ of tasks among individuals. Responsibilities which are held too long by one person, formally or informally, come to be seen as that person's 'property' and are not easily relinquished or controlled by the group. Conversely, if tasks are rotated too frequently the individual does not have time to learn her job well and acquire a sense of satisfaction of doing a good job.
5. Allocation_ of tasks along rational criteria. Selecting someone for a position because they are liked by the group, or giving them hard work because they are disliked, serves neither the group nor the person in the long run. Ability, interest and responsibility have got to be the major concerns in such selection. People should be given an opportunity to learn skills they do not have, but this is best done through some sort of 'apprenticeship' programme rather than the 'sink or swim' method. Having a responsibility one can't handle well is demoralising. Conversely, being blackballed from what one can do well does not encourage one to develop one's skills. Women have been punished for being competent throughout most of human history: the movement does not need to repeat this process.
6. Diffusion of information_ to everyone as frequently as possible. Information is power. Access to information enhances one's power. When an informal network spreads new ideas and information among themselves outside the group, they are already engaged in the process of forming an opinion without the group participating. The more one knows abouthow things work, the more politically effective one can be.
7. Equal access to resources_ needed by the group. This is not always perfectly possible, but should be striven for. A member who maintains a monopoly over a needed resource (like a printing press or a darkroom owned by a husband) can unduly influence the use of that resource. Skills and information are also resources. Members' skills and information can be equally available only when members are willing to teach what they know to others.
When these principles are applied, they ensure that whatever structures are developed by different movement groups will be controlled by and be responsible to the group. The group of people in positions of authority will be diffuse, flexible, open and temporary. They will not be in such an easy position to institutionalize their power because ultimate decisions will be made by the group at large. The group will have the power to determine who shall exercise authority within it." (http://www.spunk.org/texts/consensu/sp000760.txt )