I'd like to make a case for this extension, on the grounds that it's a complete no-brainer.

The name "PostfixOperators" makes it sound a lot more scary than it actually is. In fact it's just a tiny generalisation to the definition of left sections. You could almost regard it as a typo in the Haskell report - if it had been noticed that this rule was unnecessarily restrictive, I'm fairly sure it would have been fixed at the time.

Cheers

Simon