Has anybody here run into problems with using SimpleXML and having it produce an error in regards to zend.ze1_compatibility_mode?

It would seem according to php.net that ze1_compatibility is supposed to default to off, but a few random folks have it turned on. If you're running a script with, say, an xml language pack (as discussed in an article on this web site), you may want to look into adding the following directive, just to cover yourself in those few instances where somebody may have it turned on:

ini_set('zend.ze1_compatibility_mode', '0');