INSERT ... ON DUPLICATE KEY IGNORE

I would like to request the following feature:

INSERT ... ON DUPLICATE KEY IGNORE

This feature is to address the issue posted here of having to perform a null operation:
http://stackoverflow.com/questions/1361340/how-to-insert-if-not-exists-in-mysql

It would work much like INSERT IGNORE except that it would only ignore duplicate key errors, but support all other error types. This is contrary to INSERT IGNORE as it reports all other errors as warnings, according to the manual.