A video of Robin Hilliard's session on using MVC (Model View Controller design pattern) with Flex from webDu has been added to video.onflex.org. I attended this session and found it a great introduction to using MVC with Flex. Robin is a very knowledgeable presenter with a genuine enthusiasm for MVC.
This presentation made me realise that MVC is an ideal design pattern for most (all ?) Flex projects (regardless of scale). If you are involved in Flex development then you should have a good understanding of MVC; if only so you have the choice of ignoring it. This video is a great entry point for understanding MVC.