Here at EffectiveUI, we've been trying for a while to work out our process. We started off with something that was very similar to the waterfall and have since gotten more agile, but it's still pretty undefined. As we move towards more definition, a lot of us developers are pushing for less process and more software. We believe that the only real metric for measuring and testing sofware ideas is software itself, and at times it sounds like what we're advocating is scraping the design process altogether.
We're not, and perhaps we get a little too excited sometimes. Jeff's post is a great way to realistically approach Agile-like development with UX design in mind, and I highly recommend it for anyone in a similar situation.
The only real disagreement I have with Jeff's post is the strong distinction he makes between designers and developers. Maybe that's necessary and appropriate in other fields, but I don't feel it has to be with RIA's, and I'm not the only one - this idea is months old and already agreed upon in our community. I hate the idea of developing two time boxes behind. I want to be involved in the design and involved in the feature validation. I'm a part of this process too you know - not just the code monkey who builds whatever you geniuses think up. :) He does go on to encourage a lot of collaboration, but I want to do more than just collaborate - I want to help design!
Lastly, this is what I think of the silly made up jargon word "ideate":