Symfony2 has a big learning curve at first coming from 1.4 You'll see that everything is a ton less "automatic" which requires for somethings like a simple extra field on a form a ton of extra work. However after you get use to it, you'll love it. It took us a while to get use to it, but once you understand its approach it is very powerful and quick.
I'm coming new to Symfony from working with my own 'framework' library, cutting over my main project into Symfony. So far I'm loving it for having such clearly well thought out architecture, the guys at Sensio are excellent at sticking to their standards.
<blatant self promotion> I've started to take what I'm learning and to hack together what will eventually become a book on how to use Symfony's default framework, and then to expand on individual components.. You can keep an eye on my progress here http://leanpub.com/philrenniesymfony2