Right now the ITSM community seems to be abuzz with suggestions for open contribution repositories for ITSM knowledge and discussion. As one who has had a few cracks at this, let me assure you that if you build it, they won't come.
[Updated: let's compile a list of sites, see below]
The ITSM road is littered with the rusting wrecks of open ITSM bodies of knowledge (BOKs). Open ITIL, the ITIL Wiki, the ITIL Open Wiki, the ITIL Process Wiki, the People's Liberation Front of Judea...