A word of warning. I just updated to PHP 5.4 which broke my installation because call-time-pass-by-reference has been removed in this version. See: passing by reference.
Along with some other functions you shouldn’t be using anymore anyway. See the incompatible list.
For up-to-date plugins and software this shouldn’t be a problem since it was deprecated for a while already.
For me it notably breaks the Feedwordpress plugin in WordPress and gives a fatal error, which is annoying. A simple solution is present but you need to dive into the code and replace a few lines. See the solution here.
I fear older plugins of various kinds are also vulnerable for this problem, so I advice to check your installation locally against a new php version to see if any problems arise before your host decides to upgrade their installation!