A fair bit actually. Check out Lizard Kings. The scientist in the video, Dr. Pianka, works down the hall from me and is a very well-respected ecologist and herpetologist. He doesn't work directly on monitor behavior experiments, but he says (paraphrased) "The monitor is the only reptile that, when you look into its eyes, it's looking back at you."A very pretty lizard - and if they are tameable (or other monitor lizards are), that makes me wonder - has anyone really put effort into testing the intelligence of monitors?
Their size variation is really remarkable considering they all share the same body plan, and apparently in some cases their diets are really different, too. I'm not a big pet guy, but if I ever do look into getting one a monitor is right up there on the list.