I used Yii for a little bit while trying to decide if I wanted to use it or Symfony 2, and I just didn't like it. The page caching felt horribly clunky to me, and there was no built-in way to manage HTTP headers.

Ultimately though, I didn't decide against Yii because of what it couldn't do, but decided on Symfony 2 because of what it did do. It was just a more pleasant experience, and I never felt like I had to fight the framework to do what I wanted to do. Sure, it had a steeper learning curve than Yii (I started using it in the preview release stage, when documentation was in flux), but I feel that it made me write better code.

I think it's disgusting. It tries to use the component model, similar to ASP.NET. Even Microsoft realized what a disaster it was, and the community moving to ASP.NET MVC, which is similar to traditional frameworks.