Colin Dunn at Treehugger reports that "Discardia is a cyclical, floating holiday (it happens several times per year).... [It's a] time to get rid of things (by recycling, FreeCycling & giving away, rather than pitching it, of course) that no longer add value to your life, shed bad habits, let go of emotional baggage and generally lighten your load.... The holiday is particularly fitting this time of year, when much of the developed world gathers to celebrate through giving while consuming too much: eggnog, new stuff, and the list goes on. The latest Discardia started December 21 (with the winter solstice) and continues through January 18 (the next new moon)."
The original Discardian appears to be metagrrrl, who posted a tip a day during the past year on things you probably don't need, ranging from the highly ideological (suburbs) to the practical (printed phone books). The December index is here.
Like other culture jammers, metagrrrl can't avoid quoting capitalists in her exhortations. "Maybe you feel guilty about getting rid of that 'perfectly good' toy you don't like anymore. Stop. It may be perfectly good for someone, but that someone isn't you. There's nothing inherently wrong with you getting rid of it. Who are you worried about offending? (As the Ikea ad says 'Many of you feel sorry for this lamp. You are crazy. It has no feelings.')"
Of course Discardia, like environmentalism, isn't really anticapitalist; it just opens a new realm of profitable opportunities, like California Christmas Tree Recycling. (Hat tip to environmental economist Matthew Kahn at Environmental and Urban Economics.)