This question need to be asked in php lists though but mentioning here if anyone already have links about them.
For example
PHP Strict Standards: Only variables should be passed by reference
For production server these error are said to be kept disabled upto latest php version. but in how many version they should be converted into fatal errors or warnings?
ereg,eregi : and other POSIX Regex
These functions deprecated from PHP 5.3.0 . when this extension is expected to be removed altogether.
These questions are important for all legacy code sites.
If you're looking to find out what functions are deprecated in various versions, the best source for this information is the PHP documentation.
Check the "Migrating from .." pages under appendices for details on which functions are deprecated in each version.