The main problem with ancap is that there's nothing preventing a violent gang (a new government if you will) from forming, because everyone else is being so peaceful, and if everyone else stops being peaceful, then it it isn't ancap any more - its just regular anarchy.
Ancap will only work if there is some force to stop people from conducting acts of violence, preferably some force that isn't corruptible. So, until we have open-source peacemaking enforcement droids no such utopia can exist.
Once ancap becomes firmly established this will not be a problem, others will band together to defeat the "violent gang," if this "violent gang" happens to win it will simply be peaks and troughs of centralization vs decentralization settling on a long-term mean. Also, ancap doesn't require that every single person who owns land/property defend it himself, there will be large communities (perhaps even states) of trust where everybody acknowledges that it is to the betterment of the community to work together.
Ancap isn't feasible now mainly because the technology is hardly there to support it. Freedom of information, a transparent money trail, and the abolition of privacy (yes... I said it... too many libertarians clinging onto privacy, well the notion of social privacy is obsolete now, it is simply another element of human living that will be destroyed by civilization) must all be present for ancap to truly exist.