I've been wondering about getting contributions to a new open source product my team will be developing. There's encouragement for us to get as much support from the wider community as we're able, but I can also see this absorbing a lot of time making sure that 3rd parties located outside our office are on track regards things like code quality. Also at the start of the project we're likely to have a lot of informal discussions within the core team regarding design of the system, spikes etc. and taking these online to allow community involvement will be time consuming and I can imagine could make the discussion less effective.
There is a more human side to this which probably needs to be considered: allowing community involvement in the design process may also have its benefits regards perceived ownership of the project, and there's always a chance that early involvement could pick up on problems that the core team haven't noticed.
So the question: at what stage of an Open Source project should you invite contributions from the community?