I don't think I've ever lied in a relationship... I just can't bring myself to do it. Sometimes this gets me in trouble, but I like to think it adds just as much value as white lies and placations; if not more value. If a woman asks me to "rate" her, I'll be honest. If she asks me about her cooking, I'll be honest.
As for omissions. We all omit things to some degree. Me? I just don't care to share trivial info if it doesn't add anything. I won't omit something that is significant, though; that, I make known when/if I discover it. E.g. if a fling thinks we'll be an item, and that's not what I want, I have to make it clear that isn't the case before pursuing.
And cheating. I would never, ever cheat on anyone; ever.
How honest are you in relationships? (If we could, let's keep judgments about other people's honesty/dishonesty out of this thread. I'm just curious.)