For every new feature you need to ...

1. Say "No"
2. Force the feature to prove its value, let requester think more than twice
3. If "No" again; everybody happy, end here. If "Yes", continue...
4. Sketch screen(s)/UI prototype and get "approval"
5. High level design... detailed design...
6. Code it
7. Test
8. Tweak
9. Loop back to 7 until test passed
10. Check to see if help text needs to be modfied
11. Update product demo/tour (if necessary)
12. Update marketing materials (if necessary)
13. Update TOS (if necessary)
14. Check to see if any promises were broken
15. Check to see of pricing structure is affected
16. Launch as beta
17. Hold breath and sit back

[adopted from 37signals' thinking]