I have a very old site still on v2.4.7. I will hopefully be upgrading it in next month or so, but before then, does anyone know of any compatibility issues if PHP version is upgrade from 5.3.X to 5.4.X or even 5.5.X? i.e. can anyone think of anything that may fall over in SS v2 with these newer PHP versions?
Don't know of any particular functions (maybe ereg and split) but my advice would be to check the PHP change log
I would also check the deprecated functions as they may be used in the old version of your site or SilverStripe.
See the link below for the deprecated functions between PHP 5.2.*/5.3.* and PHP 5.3.*/5.4.*