Digimmersion are a company that create stencils for Visio for creating wireframes for Flex development; I notice that they have a great little document that explains to people how to build a Flex 2 application with Cairngorm - you can find it here. For those of you learning to develop with Cairngorm, you may find value from this 30-page article.
It's really satisfying to see that the community is now delivering these offerings around Cairngorm and Flex !
I've read this document from beginning to the end and now can say it worths spending time on it.
The best part is they describing the whole process of creation Cairngorm application on real example, and this is not another hello-world application but rather complex one.
About involving Digimmersion Flex 2.0 RIA stencil for Visio in creation of Flex interfaces mock-ups. I think you missed important point here: this stencil costs only $20 which is reasonable price for such helper.