My parents argue more often than they talk, it's gotten rather boring by this point. When I was younger, it used to scare me quite a lot - especially since one is prone to tears and the other is prone to shouting very loudly - but these days it annoys me more than anything else. Half the time I don't hear it, though, since I almost always have my earphones in with something that will block out the sound, ours is a very noisy household even without the arguing. When I can hear it, I'm prone to jumping in to tell them both to shut up, I don't care what they argue over.
What I do not appreciate either is each of them complaining about the other to me when it's just the two of us in the house. As far as I'm concerned, they're both as bad as each other and can sort their own damn marriage out, I'm not a counselor, nor do I really care. Frankly, sometimes it amazes me that they're still together...
I can relate to this quite a bit. Sounds almost identical to my Mum and Dad's situation before they divorced years ago. Only difference is that my Dad never bad mouths my Mum to me and never really mentions her at all anymore. My mum is the complete opposite and will insult/critisise my Dad whenever the opportunity presents itself. I've tried to tell her that belittling or insulting the father of your kids is going to cause some sort of psychological damage, but alas, she can be neurotic!
I'm guessing this type of issue is extremely common is Western societies. Especially over here in Britain.