I don't have guests very often, but when I do, it's almost always close family members (e.g., my parents or DH's parents) or it's close friends. We never invite over more than four or five people, and usually just two.
Special dietary needs don't really apply to the people we have over. Preferences, yes, and we always accommodate that (e.g., my dad doesn't like Mexican or Chinese food). The only thing I can think of is that DH's parents try to eat a low sodium diet in general, but they make an exception when they eat out, so we don't try to make low sodium versions of dishes. I figure if they'll eat the high sodium foods served in restaurants they can handle what we serve.
We did have an extended visit with DH's parents once (about a month I think), during which I cooked dinner every night. Because it was such a long visit, I made low sodium food (and salted the heck out of mine and DH's!).
Oh wait! My dad is diabetic and can't have sugar. But that doesn't come into play anyway, because we don't really eat sugar here... I guess if I was going to serve dessert at all, I'd make a sugar-free version or alternative for Dad so he didn't have to watch everyone else eat dessert and do without.
I guess I would accommodate pretty much anything in a small group. Large groups are another matter entirely. I guess if for some reason I wanted to invite over a bunch of people and wasn't sure of their dietary needs, I'd just make a wide variety of foods and stick a post-it note to all of the serving dishes ("no pork, gluten free", "vegan", "vegetarian", etc.). Or I'd have a list of the ingredients for everything I was making, and I'd send that out in advance of the big dinner so people knew what they could and couldn't eat. Not something I've really thought about, though...