Omar Lizardo digs up evidence from social science literature to support his advice that we should avoid "grindstone words" (hardworking, for example!)
So for the love of everything that is holy ...don’t pepper (I don’t and I have been able to fill up up three or more single-spaced pages) your recommendation letter with allusions to hard work.
Luis Von Ahn's Advice on Grad School Applications. In his set of quirky-but-good advice, there's one about what not to say in recommendation letters:
4. DON'T have your recommenders write that you are "from a good family." Unless that family has a Turing Award or two, we don't care.
Related: Matt Welsh's post on How to Get into Grad School