CC: I understand your position, classical anarchism as it were is at least somewhat outdated (the state and capitalism are not the sole origins and locations of oppression and illegitimate authority), but so is classical liberalism, Marxism, etc. and the societies we live in today are a result, more or less, of these ideas being used to structure society.
That is why postanarchism and poststructuralist theory in general is needed, because it helps us understand our current situation much more clearly in terms that don't rely on modernist Utopian assumptions (a charge that could be levied at most Enlightenment political philosophies).
In terms of actual anarchism in practice there are many examples to look at. The Spanish Revolution being perhaps the most important. And as challenge everything has said, nothing has to be absolute to be called as such. Anarchism may be perfect, ideal, utopian in theory and will necessarily not live up to this in practice, but that does not mean anarchy cannot come to be in the real social world.
Regarding Proudhon's theory about federated anarchy, no it is not a republic, but it is a democracy (anarchy and democracy are not mutually exclusive terms). There is no contradiction in terms since federated anarchy remains decentralized in its structure, with power arising only from the bottom up. Of course this is 'just' the theory, though in Spain and other places it was practiced in a similar sort of way. In fact the theory arose directly from the practice occurring in French Communes.
In terms of the tyranny of the majority which you rightly point out, Dakryn, it is potentially an issue, no doubt. However, anarchism attempts to deal with it by requiring supermajorities on certain issues, and always allowing minority opinion holders to voice their dissent. If a compromise cannot be met, those in the anarchist community who oppose an action always have the option of seceding. This is their choice. You probably think this isn't enough, and to some extent I agree, but dealing with the potential tyranny of the majority is a huge topic that is problematic in many different political contexts (most recently the gay marriage vote in California), not just in anarchism.