Hmm...if we're all planning on paying, we pay for our separate orders of food and drink. Unless we ordered something we all ate of, such as a large pizza, there is no reason to split the check.
As to paying for someone else's alcohol, my experience is that it differs, at least between Miami, USA and Norway at large. In Miami, if you've invited someone out to dinner, you're responsible for paying the full bill (including drinks). In Norway, you're responsible for paying the food, but not alcoholic drinks (as they're significantly more expensive than other drinks).
Even with these general rules, it varies from what kind of dinner it is, the available budgets of the persons involved, and what a person cares to pay for; if a person does not want to pay for alcoholic beverages, he/she should be able to upfront about it before people start ordering (heck, before they all arrive the restaurant).
Because I don't like alcohol and particularly not people who've had too much of it, I make it clear that I will not serve alcoholic beverages when I invite people for dinner (though guests are free to bring some for themselves, essentially BYOB).