Are there any known points to be careful about buffer overruns in PHP? Currently I take an email address from a form, run it through preg_match to check it's only a single address, call the mail function with it, and store another load of form data in a database using PDOStatement::bindValue().
Anything to worry about?
If you are asking if it's possible to write code in PHP that contains buffer overflow vulnerabilities, then the answer is no. You can't have those in PHP, it manages the memory for you and you can't directly alter the memory. The only scenario is that PHP itself has a (security) bug, which you can mitigate by keeping PHP up to date.