I have several live Drupal sites running on an Ubuntu server (10.04), Apache 2.2 with PHP 5.2.3-1. I recently started the work of setting up a test server that would be as close as possible to the live environment, but I stupidly didn't check the PHP version that Ubuntu installed when I did an apt-get install php. I've now had my test server up for several weeks, and just realised that the version of PHP on my (edit: test) server is 5.3.2-1.
Part of the reason for the test server setup was to try a Drupal upgrade: 6.17 -> 6.19, and with it a bunch of modules, incidentally fixing errors along the way that were related to things that no longer silently fail in PHP5.3.
So the question is: will I regret not having the same version of PHP on my test server as on live? Instinct tells me that having different test and live environments is a Very Bad Idea, but perhaps it's not such a big deal in the Drupal world (along the same lines of reasoning that not having version control is a Very Bad Idea, but that is a difficult task for CMS users). I really don't want to mess with my (very much working) live environment if I don't have to; is it a huge chore to downgrade the PHP version on my test environment?