I use them constantly to find the actual data source for probate, code enforcement, sort by type of property, lis pendins, zombie properties, power of attorney, divorce, evictions just to name a few. 

You could also check out the city data forums.

I told her what I had been thinking based on listening to and observing the data that some of the countries MOST brilliant economic minds are quietly saying in closed door meetings.

To meet growing consumer interest, more Multiple Listing Services (MLSs) are incorporating data entry fields to identify a property's green features; 43 percent of respondents report their MLS has green data fields, and only 19 percent do not.

getting more rent aside, a house with Solar is worth more than one with out and has been proven so by sales data.  

I want to know where the data inputs and calculations are coming from.I am approaching this from a basic investment standpoint.  

I'm such a data nerd.

Read about them on Wikipedia, City-Data, Local Newspaper, Local Business Journals, etc.

What is his current data; rent, vacancy rate, other expenses, and NOI.  

creating lists, answering calls... data mining