James Ward wrote about top 10 Adobe Flex misconceptions. Here is a short list of those, complete arcticle at ultrashock.
1.Users need to install something new to run Flex applications
2. Flash Player is 100% proprietary
3. Flash is for designers, video, and annoyances
4. Flex is not for enterprise or business applications
5. Flex is expensive
6. Flex applications require a special server
7. Flex is hard to learn
8. With Flex, I will need to rebuild my entire application
9. Flex breaks normal browser functionality, like the Back button
10. I can do everything Flex does with Ajax
Another short but very useful introduction for total beginners in Flex from Sujit Reddy G.