Andrew Edwards just posted a case study on his team's experience in using open source Flash tools as part of their development process on the PlaceAd RIA for TradingPost.com.au last year.
In the study, Edwards mentions how their use of open source tools saved them over 110 hours in compile time and allowed them to integrate better with their overall .Net development process. He also relates how it resulted in fewer bugs, "better code" and a "better development environment".
I was recently at Mix '06 in Las Vegas, courtesy of Lynda.com, along with a group of fellow Flash developers as part of a Microsoft-sponsored initiative to both expose some of us in the Flash world to Microsoft's new Expression line of products and to get our feedback on them.
The Expression line includes the incorrectly-named Expression Graphic Designer and Expression Interactive Designer as well as the Dreamweaver-clone Expression Web Designer.
Still, though, I'm so happy that, working with Flash, I haven't had to worry about browser compatibility issues for the longest time.