I have written a comparison of three PHP frameworks: CodeIgniter, Yii and CakePHP.
http://daniel.carrera.bz/2009/01/comparison-of-php-frameworks-part-i/
It is positive of CodeIgniter. This comparison is the result of several weeks of study of all three frameworks, starting from almost no initial knowledge.
Are you dissatisfied with most comparisons because they are too superficial? Me too. So I tried to make a positive contribution by writing a review/comparison that is thorough, balanced and clearly written. No framework is the absolute winner, but CodeIgniter did very well.
It took a lot of work to write this. Now I hope that new users can find it, and that it is useful.