Scott Farquhar one of the co-founders of Atlassian said this best in his talk at Business of Software this week. Which I'm paraphrasing from memory...
If you're co-founding a startup equal shares is the way to go you should be doing this with someone you trust and can work with and squabbling over pieces of a worthless asset at the start is a sidetrack from doing what matters.
I'd add that vesting is never a bad thing but if you are so worried about people not contributing you shouldn't be starting a company with the person.
