Just back from giving an invited talk about Puredyne at an Openmute event about "Digital Innovation for the Arts". Claude and I introduced Puredyne as a live-distro tool for real-time multimedia art etc - but we also focused on thinking about lessons from the open-source way which might apply generally to artistic projects who want to move towards open, "co-creative" ways of working.
One thing that is not always said about open-source communities is that there are typically multiple loosely-connected groups, and the loose connections provide the richness that allows projects to thrive. There's even research that seems to bear out this point (e.g. Méndez-Durón and García 2009). So don't focus purely on creating "your" community, but ensure that you enable connections outwards, both in the social interaction and the technical underpinnings (e.g. the reuse of data). This is partly why Twitter is more important than Facebook for some things: the openness of Twitter allows ad-hoc and temporary connections between people who otherwise have no bond.
The loose connections are related to a really useful general concept called peripheral participation. This basically means that in any successful community, yes, there will be die-hard committed members, but there will also be people who drift in and out and may make some small contribution (e.g. a single comment on some issue). It's really important to enable this peripheral engagement and allow people to move from a mild occasional involvement to a deeper involvement - because typically that's the only way that your community effort will maintain the critical mass to carry on. (The availability of routes from casual to hardcore member [and back again] is one of the main insights of the communities of practice model of social organisation.)
Also, since people can "drift" in and out of deep engagement with any community, the focus and aims of that community can evolve - don't assume a constant unchanging core. There must be a focus of some sort, otherwise there's no cohesion of common interest. There doesn't have to be a "leader" (although there can be) but there is still some structure, based around the social network of the community core members - meaning that although there's no hierarchy, there's a difference between a "peripheral" or "drive-by" contributor and a long-term contributor which emerges in the social influence they have in the community. Given that, it's important for "core" members to allow and encourage casual involvement, providing ways for people to get more or less involved as they wish. All successful community projects have a mix of casual and more committed members.
Open-source communities are typically spread across the world and communicate online. To make this work, fast casual communication channels are important: traditionally geeks use IRC chat, but for less geeky projects you could use Twitter/identi.ca or Skype, for example. These enable quick little chats like "Natalie did you do that thing?" "Yes Claude's got it now" - 'disposable' communication which enables speedy co-working.
But many successful open-source projects also have real-world meetups and this has many benefits. It might sound defeatist to say that online communication somehow isn't good enough and that people need to meet in real life, but it's not quite like that. Online communication is great for most of the co-ordination that open projects need, but getting together for a face-to-face session for a couple of days (which coders might call a "hackfest" or "code sprint") enhances this in a couple of ways. Firstly it provides a concentrated time to think/discuss issues in detail, in a "high-bandwidth" way and with few distractions, and there will always be things that need that kind of focus. Secondly it really helps to build personal bonds between people, allowing wider discussion and building the kind of understanding which will improve the remote online communication in future. Even if you're planning something which lives entirely online, if you want to build a strong community then "in-real-life" meetups of some sort are a good idea.
Another lesson from open-source and free-software is that of openness in ownership. I've seen a few examples of "crowdsourcing" and "co-creation" and there's a fuzzy boundary between the kind of thing which is essentially a focus-group or survey but done in a social-web-style, and the kind of thing which expects more creativity and focused input from participants, essentially opening part of the design process up to allow non-professionals in. So in the latter case there's an analogy with the open-source world but one lesson that should be remembered is that if people are really putting constructive effort in, then they need to be treated fairly in terms of their stake in what comes out.
last.fm is a great example of this, a business which was built upon gathering data about musical listening habits - but one of the keys which enabled last.fm to develop as strongly as they did was that the resulting data wasn't locked away in some company safe, it was republished under a Creative Commons license. This meant that users could feel confident that they were not being short-changed, that they were not volunteering personal data simply to some corporation but to a communal dataset which can be used for other purposes. So if "co-creation" is to continue as a way of doing things then it must treat the non-professional co-creators fairly in the ownership of the output.
This openness often ends up with some form of available "open data" which people can repurpose for other uses. This can be quite intimidating for some organisations, a partial relinquishing of control, but its consequences are often that some other group can connect to your data and do something great with it that you couldn't have predicted. See BBC Backstage for one initiative which encourages this - and think back to the concept of multiple loosely-connected groups, which stimulates the development of communities. Publicly open data is one way organisations can lay the foundations for such connections to happen.