I'm midpoint of Season 8 in Friends and can think of at least 3 things HIMYM and Big Bang Theory have stolen..
Friends was the first *massive* sitcom. All new sitcoms are compared to it. I prefer HIMYM and BBT but of course there are tons of similarities. Friends is awesome, I've probably seen every single episode 5-10 times each. It's one of those nostalgic feel good shows for me.