So I need PHP 5.3.2 for my slice. For those of you that have needed you probably found that this is a pain for packages. As a result of most of the google attempts I just build my own packages. You can find them here: http://pe-ell.net/rpms.html
Surprising everything worked great out the door afterwards. Tested all of my php sites and they worked fine. I need to change my logging level though since I'm getting lots of PHP Deprecated and PHP Warning due to the upgrade. Hopefully this will help others.
Also make sure you have date.timezone set in your php.ini and you should probably change your error_reporting to something like this: E_ALL & ~E_DEPRECATED & ~E_USER_DEPRECATED & ~E_NOTICE
No I didn't. I use roundcube. I have found that I had to tweak a couple open source projects that I have running. LifeType I just gave up on and wrote my own blog to replace it. They use very basic names for all of their classes ("Locale","Cache",etc) without any namespace and it conflicts with core classes. Most of my PHP stuff (other than LifeType and RoundCube) is older so not sure if I'd notice potential issues.
I did end up upgrading to php-5.3.2. Squirrelmail works fine as well as Wordpress. I used your method to upgrade initially and finished with updating via CentALT since I needed the current php-fpm.