We never fight... I'm just wrong 40% of the time, inconsiderate 40% of the time, and asleep the other 20%.
If I had to guess, I'd say we have a major disagreement/fight/issue about once every 4 or 5 months. It's all in how you approach though, if you're both rational about it, you can actually build/learn/grow from it and it's helpful. If you both are screaming banshee's who throw dinner plates and say things you don't mean, the original issue isn't resolved and you've probably created many more.