Funny, I walked away from Flash/Flex with the exact opposite impression. Data binding is good in theory but horribly slow in practice - any time something changes it dispatches a gazillion change events to be processed, and debugging problems with bindings can involve going really deep down the rabbit hole...

It's one of those things that seems nifty from a developer convenience point-of-view but results in poor user experience - pretty much every Flex app I've seen that made heavy use of bindings ran horribly slowly.