We try *hard* to work to prevent suspensions...certainly bans.
The person suspended or banned is told the length of time they'll be suspended/banned for. If a person is banned completely, their account is rarely ever activated again. However, with a suspension, it's up after a predetermined amount of time told to the member. Alot of thought and consideration by the moderation/administration team is given to the circumstances surrounding the discussion of suspensions/bans when they occur which I'm happy to say isn't often.
A ban here is uncommon, but does happen in extreme or continual cases and rarely without warning.
If you have more questions, don't hesitate to shoot me a PM.
KD