[vanderwal]

OmniGraffle has become my preferred IA diagramming tool. I like it much more than Visio as it gets out of the way. I can work more quickly and in OmniGraffle than Visio. The latest versions of OmniGraffle work quite well iterating back and forth between teams/others using Visio (it begins to break after 3 rounds). I have not used Axure, so I can not comment.

While I do much of my wireframing in XHTML/CSS I use OG to work through iterations of steps needed for interactive interfaces. I use OG for quick diagramming of workflows and relationship diagrams. I use OG for nearly all of my graphics for presentations for client work and other presentation needs (using Keynote almost exclusively).