If I can just add to the chorus of praise for Louis Proyect's lucid post on utopianism...
Another problem with ParEcon is that not only isn't it, from where I'm sitting, very inspirational (can you imagine Albert and Hahnel writing a "Looking Backward"-type novel?) but it's not much use as a guide to actual politics. Does it give us any principled basis to support single-payer health care, say? Does it give us any basis for any concrete political action other than joining Twin Oaks?
As for Twin Oaks, our Paris Commune, it's basically a subsidiary of Pier 1. The day folks shopping for throw pillows stop picking up a Twin Oaks- made hammock as well, that's the day that particular experiment in participatory economics comes to an end.