Depends so much on the situation. We've organised 50+ group holidays over the years for students, friends, families and a mixture of all- including skiing holidays. With large groups, we've always gone for all inclusive option and everyone pays their own costs, depending on need (for skiing for instance, some make their own way by car, others fly + transfer, some need lessons, some need to hire skis, boards and or boots, etc, and some do not ski but come for the scenery and company). With close family, again, that depends. If someone in the family is going through a bad patch, their cost is taken by others, if we have a windfall or for v special occasions (like OH's 70th next year) - we will pay for all- but others will make sure to chip in with special meals out or in other ways.
When we go with another couple, we take it in turn to pay for meals and petrol, and keep receipts, and make a quick tally at the end to make sure there is no great disparity. Sometimes we have a kitty where we each put £100 and use this for all expenses and put more in when necessary. It all works out in the end.
For guests here at home, as we live abroad- we have a 1 - 2 - 3 rule which everybody likes and adheres to- we cook the first night, we go out and go Dutch the second, they cook the 3rd, and so on, more or less. It's brilliant as we all muck in and there is no resentment or embarrassment re being a slave to guests or a burden.