After much discussion and contemplating, the staff makes a decision on the length and severity of the suspension or ban factoring in the member standing, the nature of the offense, what caused it in the first place and many other things.
For example repeated vulgarity and profanity, porn, etc will usually result in instant permanent banning.
Infractions of a milder nature may be subject to a 30 day or less ban and sometimes people just need to cool off from a heated discussion which could be say a 24 or 48 hour ban.
One more point I'd like to bring up: The Staff work really really hard to do everything possible to resolve situations and issues BEFORE there are any bannings. We want everyone to be a part of this community if they are willing to be calm, friendly, and helpful.
Unfortunately some people, either knowingly or otherwise, post their opinions in a very abrupt and sometimes offensive manner. We usually Private Message these people multiple times with warnings, and if they still don't adhere to our rules they are issued a ban to the extent of the violation, as Terrie mentioned.
If you haven't received any "reprimands" or "warnings" publicly or via PM's from a Moderator asking you to stop doing something then you're not even close to being banned.
Also, if a post is edited, or removed entirely from a moderator, that's usually a REALLY good hint that the members shouldn't have posted it publicly.