Moodle 2.0+ recommends the use of the intl-php extension. I know that someone also added a tracker (or whatever they are called) about including a self-test to check php versions and to push users toward php 5.3 on the grounds (as far as I recall) that it was quicker.
Taking the hint, I upped my php from 5.2 to 5.3.
I didn't have a clue how to get and use intl-php and couldn't make head nor tail of the instructions in moodle docs, so I spoke to Hostgator (my hosts) to see if they would sort it out for me.
This evening, after chasing them for progress because intl was still showing as not being available, I got this response...
"I have escalated this to an L2 admin and they have found that this function (intl) will not compile with php5.3. There seems to be no issue with 5.2. I see that you had just upgraded to PHP 5.3, was there a conflict with your moodle version and 5.2 or was the upgrade just recommended? Would it be possible to use php 5.2 instead of 5.3? They can install it (intl) with that version of php instead of what you currently have."
If the above is correct, does this mean that there will be a conflict in future between wanting the intl extension and also running php 5.3? Anyway, now I guess I have to downgrade to 5.2 again to get intl working.
