Wireframes a breeze in Modeler for SP
IntraNet Factory's Modeler for SharePoint was a breeze to both understand and use. No big learning curve here, after watching a couple of videos and poking around, I was up and running in under 20 minutes. Fortunately my SP needs ran fairly closely to the standard functionality of SP, and so the Modeler for the most part was able to wireframe what I wanted. If your needs run towards a more customized SP, Modeler may not offer what you need.
One drawback was the inability to add a page without it showing as a tab on the top. The work around was to hide it under an another page. I would have also liked to be able to have a workable "Quicklinks" section as well, since this is more of a functionality part, instead of typical content that should have placeholder text.
Overall though, a great tool. My audience was appreciative of the wireframe mockups and didn't get caught up in content, which is exactly the point.