This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
In general, developers lean toward familiar design patterns as they cross language and framework boundaries. This doesn't work great for all patterns. If you attempt to do MVC in Flex you may be making it harder on yourself and possibly not taking advantage of having a stateful user experience by doing so with an event-based framework like Flex. I also think the code could turn out a little messy. Here are some alternatives to MVC for Flex and relies on the developer to actually design the code without utilizing a framework. Not that i'm against frameworks. It's just that you may not get the right pattern by leveraging a framework.