I posted about 161 Gambier St and what the neighbors have had to go through to get the city involved in order to get the owner to take responsibility for his property.
One neighbor wrote into the Portola Yahoo group concerned about monster homes going in, owners being pushed off their property by "busybody" neighbors, and the diverse character of the neighborhood being compromised. Well, one thing she forgets is that the house in question, like many in the city, were built in the '40s, and the city is very keen on maintaining old neighborhoods in their historic appearance (a double-edged sword, as anyone who's tried to update their home has found out). So, I think that her fears are misplaced about a giant McMansion being built on the site.
In my Silver Terrace neighborhood, we had a similar house that was uninhabitable and a danger to kids looking for a spot to play - the windows were boarded up, the roof was missing, and the garage door unsecured and inviting to a curious child or shelter-needy homeless person.
Over the course of the past couple of years, the property slowly transformed, and now there is a family living in the house. Through observation of the people on the block who seemed most interested in the property, it looks to me like a resident who owns a house up the street also owned this derelict property and ended up restoring it so that their parents could live in it.
So (duh!), a property owner who cares about the neighborhood that they're living in can make a huge difference.