Cake is an excellent PHP4 compatible MVC framework with a very stable code base. The testing culture and extremely talented developers around the project is a huge reason why. I started using Cake 1.2 when it was in its infancy, and was able to keep pace very easily with 1.2 upgrades until its final release (and beyond) over a 2+ year period. This is a serious accomplishment in stable API software design.
That said, any serious development with CakePHP will involve becoming familiar with caching. Fortunately, the PHP language and the CakePHP framework make this integration easy.
I look forward to what the CakePHP team have in store with a PHP5-only compatible release. I expect only great things.