My parents were part of a group that did the first kind. There was a group of 6 couples. Every month or so 1 or 2 of the couples would get together to plan a meal. They'd pick the theme and research & select the recipes. The recipes were then distributed among all the couples. They kept track of who did what dish so one couple wasn't always stuck with the expense of the (usually) most expensive main course. On the appointed day they'd get together at one of the couples homes and bring the dish they were assigned. They, and all us kids, referred to this as the Gourmet Group. They kept this up for 10-15 years. Eventually, they started going to restaurants more frequently. Now, one of the couples is divorced (the wife & new husband stuck with the group), two couples live out of state, and the others "snowbird". But they still get together (if not the whole group than 2-4 couples at a time) a few times a year.
We've talked about doing a potluck dinner, but giving everybody the recipes we want them to make rather than making it truly "lucky." I've heard of people doing this before. I've held off on trying because, well, it seems a little gauche to tell guests what to make and what method to use to make it. We've also talked about the same idea but telling people what generally to bring without giving them an actual recipe, or telling them to bring a side dish/dessert/appetizer that fits with whatever theme the meal will have. Anybody tried this?
I have done the second kind. For the last Thanksgiving I assigned various tasks (bring a green veg, bring dessert, etc.). Actually one gentleman is particularly cool about this. He is part of one of the aforementioned family friends (see above), who retired a couple of years ago. Ever since then he's been in charge of the kitchen. He's not very creative, but you can give him any recipe and he does a very good job of it (I think being a retired pharmacist helps with following the recipes, he's like a chemist in the kitchen). So, when he offered to make dessert he also asked me for a specific recipe. I gave him a pecan pie recipe I had been meaning to try - it came out very good. He's also learned to make many of the dishes his wife is famous for at holiday time (and he makes'm better).