I've found that in most situations, a waiter/waitress will ask if folks want separate checks if it looks likely they'll need it. If it's just me plus wife plus kid, often they just set one check in the middle, but if there are any other adults, or if it looks like 2+ non-romantically involved adults, they usually ask "one check or separate" before bringing it out.
I've never had a friend get offended by this. I'd venture to think that most people would prefer separate checks when out with friends, since, at least in the US, giving cash, or sending money to the person paying is more difficult than just paying your check yourself.