It sounds great, but of course, being tired and busy parents soon turned to the more generalised 'Good job!' And why not, it was still achieving the goal of praising the actions of the chosen actions of the child, rather than risking the child internalising the idea of being intrinsically 'good', or conversely 'bad'.
Well, except for two things. 'Good Job' is as non-specific as 'Good boy' or 'Good girl'. The child doesn't know exactly what they've done well. For example a child is asked to help their parent rake autumn leaves for which the child receives a rousing 'Good Job!' What was it the child did well, was it listening the parent? Maybe it was how they held the rake? Maybe it was because they didn't smack the dog with the rake? How is the child supposed to know which of their behaviours is the 'good' one, how are they supposed to know what to do next time to receive the enthusiastic 'Good Job!'
Then there is the other thing, the ubiquitous 'Good Job' has become white noise. It is said so often that children may not even be hearing it, no matter how excitedly it is said. Young children apparently don't hear instructions telling them not to do something. If you tell a child not to run, they hear the verb first, so they hear 'run'. It has something to do with children learning nouns first, verbs second, and then all the little parts of sentences like prepositions, articles etc. So, to get a child to stop running away, instead of saying, 'Don't run away', where the child is more likely to hear, 'Run away', consider saying, 'Stay with me'. Apparently, they'll register the word 'stay'. Um, where was I? Oh yeah, so it's important to consider what children hear, and if they are told 'Good job' 50 times a day referring to who knows what, it will fade into the back, pushed aside by far more interesting words, like verbs.
Now I hear it all the time, it's on tv, the lady down the street tells her dog, 'Good job' for walking nicely on a lead - actually it's probably quite suitable for dogs, as they're less likely to put much meaning into, 'I really appreciate how you are walking nicely next to me'.
Bosses could learn something from this as well. Instead of just saying to the employee who hands in a report, 'Good Job', or 'Thanks', or 'Well done', why not saying, 'I appreciate the time you've committed to doing this' or 'Thanks for getting this done so quickly'.
Hey, it even works with partners. 'Thanks for picking up the kids, I wasn't expecting to get stuck in traffic that long', or 'I love that you've paid attention to the sort of washing powder I prefer'. Yeah, yeah, seems is bit much, but how are people supposed to know what they've done well if what they do well isn't specifically acknowledged?