I want to set something straight. Pernil, a dish popular in the Caribbean countries from Cuba to Venezuela as well as in Brazil, is made with fresh ham. The name of the dish shares a root with the word for leg in Spanish and Portuguese, and I believe it's the Catalan name for ham.
Why is this important? It seems that all recipes to be found in English for pernil use pork shoulder, a very different cut of meat. True pernil recipes call for the fresh center or shank portions of the pig's hind legs, which is a much leaner cut that requires roasting at a pretty high temperature until it's golden and just cooked through -- the same way you'd roast a lamb gigot. The seasonings vary, but oregano and garlic feature prominently in general. In my family, we use orange juice to make a pan jus.
Do I have anything against pork shoulder pernil? Not really, it's only that calling it pernil makes me cringe a little. The truth is that roasting a heavily seasoned piece of pork shoulder at 350F for 3 hours is one of the best ways to produce juicy, flavorful pork that will stay together while slicing. I might even like it better than true pernil.
Pork shoulder pernil was probably popularized by Puerto Ricans in the United States. I must admit that, like most Puerto Rican bastardizations of the Spanish language, this one is quite luscious.