
While I am still a big fan of Omnigraffle for mock-ups and prototyping, I am aware of how cool Axure RP is and how it makes sense from an enterprise standpoint.
When I made the changeover to Macs about 3 years ago, I was disappointed that my Axure software could not follow me (I like to keep several tools in my toolbelt so I am ready to hit the ground running in any new contract)
Just today, I got the notification that Axure now has a Mac version of their design software
Its available for a free Trial download:
http://www.axure.com/downloads.aspx