In a recent post to his blog Marco Tabini talks about the "monkey on the back" syndrome that affects so much of the technology projects these days. His example for PHP? register_globals.
One such example is the register_globals setting in PHP which finally managed to get deprecated in PHP 5.3 (and, the way things are going, may never disappear altogether) after much fighting and gnawing of teeth. [...] The existence of register_globals is problematic in many ways, but it is consistent: as long as you have a version of PHP that supports it installed, you will have the opportunity to use it1. When it is discarded, it ceases to exist, so that rewriting your code becomes a prerequisite to upgrading to a new version of PHP.
He also relates it to a <blink> tag - something that really shouldn't be used any more but, because someone decided it was a good idea in the past, several browsers have included support for it. The moral of the story? Well-planned standards are a good thing.