How much percentage does a developer have in an IT-startup?

How do you distribute the shares among participants of IT-startup (Web-system)? What is the common world practice?

For example, there are two participants:

the person, who made idea and will do all marketing work

and the developer, who formalized specifications and made the web-system itself.

What distribution, in your opinion, will be fair?

Gets asked a lot, and the short answer is "it depends"

These may help you:

Forming a new software startup, how do I allocate ownership fairly? Internet startup - ownership share - developers vs biz people? Fourth co-founder but first developer