Not to bump an old thread-- but this really would be a nice feature.
I'm not a moron-- I completely understand the permission system and its inheritance (been dealing with forums for over 10 years now), but still would really benefit from having a duplicate function. As it is, when I make new groups to classify users with the same permissions, it is tedious. I realize it's not necessary but that is beside the point.
I have searched long and high and all I can see really is people Hell-bent on wasting time suggesting about how unnecessary it is, but still not budging on adding the feature. I'm a software developer myself so I can understand the "laziness" factor ("cba"), but with enough customers requesting it, I think it should be something considered in the future.
As it is, I'm stuck either wasting my time manually setting the exact same permissions, or trying to decode the way XF stores permissions in the database and making an SQL query to copy the permissions to the new group, which I'd much rather avoid.
Just my two-cents.