Andrew,
Through the years I've pushed pretty hard on the boundaries of what to grill. I recall attempts to grill fava beans, watermelon slices, and chocolate souffles, for example. In each case I had enough success that I'd do it again, especially on a gas grill. I find that the smokiness of a charcoal fire doesn't complement fruit or chocolate, and for a souffle you really need the evenness of precise heat that a gas grill provides. To me, a grill can operate very much like an outdoor oven. If you working with indirect heat, I can't anything you couldn't bake or roast on the grill, and with direct heat the number of options grows longer and longer. A few years ago I avoided grilling little pieces of food like pea-sized scallops or rock shrimp, but nowadays, we can use perforated grill pans to grills those kinds of things. Now some guys have told me that they want to fry food on the grill, as in heating up a pan of oil on the grate and frying chicken or calamari or something like that. BAD IDEA. THAT WOULD BE REALLY DANGEROUS. But other than that, I'll grill just about anything.
I hope you get my book on Fathers Day. If any questions or comments come up, feel free to "friend" me on Facebook and let me know what's up.
Thanks,
Jamie