Flex: 3 months in
It's a pity flex is an Adobe product. Don't get me wrong, I'm loving flex, however if flex/flash was an open source standard it would have replaced html years ago.
Having said that It wouldn't be such a awesome platform to build from if it wern't for the likes of macromedia & now Adobe.
I've only experienced flex for just over 3 months, however I love just about everything about it. I could ramble about it for hours, but I won't bore you. A quick search on google provides with plenty of information.
All I will say however is that if your in the business of making web based interfaces (for either web applications or web sites), then you should check out flex. As someone who has had a lot of experience with making html/css/javascript work cross-browser, it's a breath of fresh air..