[wisty]

I'd say 50/50 if the programmer works for free (and you bring something to the table), up to 90/10 if you pay them a decent salary. If you pay a full salary, you don't need to justify your involvement too much, though that can be a problem in itself - the tech guy might not really think too much of you or the project, and just wants the paycheque.

If you were pitching to a bank or VC for funding, not a tech guy for his time, what your pitch be? Domain expertise? Your existing IP? Your UX design skills? Your sales skills? Your organization and drive? Your killer business plan? I'm assuming there's a market for the product, but you need more than that.

There's not much justification for less that 50%. The only reason for you to take less than 50% is if you won't be contributing much, and if that's the case, who would want to partner with you? Or if you get a developer who is really impressive, in which case you could offer them more.