FLEX is free.
First of all, great news, Flash 9 has been released for Linux. That has many implications, one of them is that we can develop Flex now also on Linux :D.
Next week I will be at MAX and I just wait to be there. As it is hold in Las Vegas the conference it will be great.
There are some things that are happening and should be checked out:
- a presentation of Flex and Ajax working together on top of Java to create very powerful applications by combining the best features from the two worlds
- Apollo - a cross-platform runtime being developed by Adobe that allows developers to leverage existing web development skills (Flash, Flex, HTML, AJAX, PDF) to create and deploy rich Internet applications to the desktop.
- Acrobat 3D
See you there.

From what I can see, Flex is not free. Where did you find it was free?
Well not all of it. Flex Builder is not free, however Flex SDK and language pack is free and Flex Data Service Express is free (quote: The Express edition is a free, non-expiring commercial-use product for applications deployed on a single machine with no more than one CPU.).
If yo go to http://www.adobe.com/downloads/ (registration is required) you can see all of this.