I've only been banned once over a disagreement with the manager of another sim. The ban was eventually lifted after we both had some time to cool off. I generally try to behave such that it's not an issue.
On the other hand, I've had to issue a number of bans from a sim I help staff. Most of the time, people get IM'd first to be told what the problem is so they can correct it, if that doesn't work, they are sent home, again with an IM as to why and what has to be changed for them to be welcome. If they come back and continue doing whatever it was that got them sent home, then they get banned for some amount of time. This obviously doesn't apply to outright griefers (rare) or things that blatantly violate the SL TOS. Those get immediate bans + ARs.