I think it's important that warnings remain. This is because if they disappear after time, people are more likely to break a rule knowing that they just have to wait until it wears off over time. It can seem a little harsh, but its for the protection of the community.
I feel like it's important to point out, as vic said, every mod is different. We all have a little bit of a different way of seeing things. Some of us may be a little more laid back than others, and we all have different modding styles. Personally I'm a bit more relaxed, but I will certainly tell you when the line is crossed. But do remember that we are people too, we take measures to make sure that anything we do is justified and fair.
When it comes to "ignoring a mod" we don't usually resort right to warning someone, generally we'll tp to them or kick them to get their attention, cause much like some of you, we too can get "builders vision." If you think something is "borderline" to the rules, you can always ask a mod through PM's before saying it. As mods we love it when you ask questions to better understand the rules, because it makes you a better member of the community.
I want to leave off with what warped said before me. Know who you're talking to. Everyone has a story, and everyone has a comfort zone. If you think something you say might not be comfortable for someone just don't say it. If it must be talked about (and doesn't break the rules), make sure you do so with politeness, respect and in the proper chat. If asked to drop it, drop it. Remember, Do unto others as you'd have done to you!
Have a good one!
~Scoobs