Po Bronson, (co-author with Ashley Merryman of the great book "Nurtureshock") wrote an article a few years ago called "How not to talk to your kids" about the pitfalls for kids of receiving certain kinds of praise.  It was based largely on the work of researcher Carol Dweck.   

The article is a great read and the research is an example of interesting social science (that doesn't rely on over-interpreted fMRI images).  The upshot is that kids, probably all of us, need to be encouraged to view intelligence as maleable and process-related rather than static and inherent.  It is a good way to avoid trapping kids in what Alice Miller called the "drama of the gifted child," the need to protect a false, perfect image of one's self from failure.  "You worked hard" encourages us to try new things and, as the incomparable Ms. Frizzle says, "Get messy.  Make Mistakes."