The usability lifecycle argues for an iterative design process. This is totally where my head is at these days – apparently I agree with Nielson on something.
Still, all three of these methods – iteration, waterfall, and just-do-it – happen at some level of granularity in a project. For example, design may begin with a just-do-it idea, because you have to start somewhere. The design process may happen iteratively, then be “waterfalled” (sorry, I know that’s not a word) to a shop to be built (and this whole process may be repeated iteratively). So when discussing this we need to talk about the scope of activities the process addresses. Nielson is discussing it at a project level, but when you’re actually doing it, it ain’t that simple.