stay up-to-date with PHP

You could use a PPA to stay up-to-date with PHP. I use:

https://launchpad.net/~ondrej/+archive/php5 

It's now on 5.5 and also includes Apache 2.4 update. For Apache 2.2+ PHP 5.4 repository, see the bottom of the answer.

If you want use this PHP, do this:

ppa:ondrej/php5  (Click here for instructions on using PPAs.)

sudo add-apt-repository ppa:ondrej/php5
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install php5

If you don't have add-apt-repository binary do the following:

sudo apt-get install python-software-properties

Precautions:

• Are PPA's safe to add to my system and what are some "red flags" to watch out for?

For Ubuntu 12.10

Ubuntu 12.10's official repository is updated to PHP 5.4. You should use the main repository package if you can. To do this, just install PHP5 without enabling any PPA.

PHP 5.4

Prepackaged latest PHP 5.4 now resides in separate PPA: ppa:ondrej/php5-oldstable