Well, according to the latest blog-post (http://blog.secondlife.com/2008/09/04/second-life-and-ad-farms/), LL are considering zoning. However, it begs the question of how we go about doing this. I'd like to bring attention back to an JIRA issue I posted regarded automatic zoning based on parcel-settings:
http://jira.secondlife.com/browse/SVC-603
At it's simplest; if the majority of parcels in a sim are residential, then sim is considered to be residential and thus is governed by a special residential terms of service, defining what is and is not acceptable in a primarily residential area. Likewise, a sim that is mostly commercial will be considered commercial.
The idea here is that the rules will change with the requirements of the people in sim, so if you're the only person with a house in a commercial sim, then you may consider moving, as a commercial sim may (for example) permit forms of advertising, however you're not completely shut-out if you want to stay. Likewise a business could run in a residential area, provided it isn't obtrusive in any way to its neighbours.
In theory the issue would allow us a flexible zoning scheme, rather than LL having to go around defining each area and us being stuck with whatever is decided.