Keep conversations focused. Move off-topic messages to a chat section. When an on-topic thread branches, change the subject title. But let the chat section be for real chat. Don't discourage people from talking about their lives, cats, kids, cars, etc.
People are more than just customers.
Sysoping requires a certain amount of housekeeping, but doing it diligently can pay off. Archive discussions that you know will happen again and again, and turn them into FAQ files that new users can be referred to. Such freebies are incredibly remunerative, because they give happy customers a reason to return to the site often. Not only is the assisted customer more pleased, but such community activity has a positive effect on marketing, as well. That sounds a lot like marketing.