This recent statement is key for the discussion:
On 7 Sep 2013, at 09:25, Mark Roberts-Barter <[address removed]> wrote:
I am putting as many spare hours into it as I can because I believe in the proposition enough to consider it a safe investment of my time.
You have to ask yourself this.
Does an entrepreneur offer equity for spare time work or is the expectation to contract a developer full-time in exchange for the equity or being named an inventor in any filed patents? That is, does the proposal for sweat-equity allow the developer to find sufficient funds to make rent, pay bills, contribute to mortgage etc, however that may be.
Remember, everyone has day to day expenditure of some sort and that however marvellous a proposal may be, only a small subset of the talent available will ever be available full time for free, even for a week. So be clear in your proposal that you appreciate the 'reality on the ground' and many more developers may take the steps to form that first relationship...
best of luck :-)
designer : developer : consultant
...hardly damaged by a decade of work in California at all....!