Sure; the same ones as for sites built in HTML, CSS, Javascript, ASP, etc., etc.
PHP is server side technology. Any issues with browsers are the result of what you are telling PHP to say via HTML/CSS/Javascript, not PHP itself.
AAMOF, PHP could be quite helpful in this regard, perhaps (as an example) detecting a user-agent string and including a different stylesheet depending upon which browser is requesting the page....
Of course, this concept could be misused as well... witness Microsoft's treatment of Opera.... :rolleyes:
