We saw this on Chicagoist, and it came with a warning of the possibility of major time disappearance. They are right - consider yourself warned, too.
Zillow has an interface based on satellite maps, that allows you to hover over Chicago and zoom in close enough to view specific buildings. Then you can start clicking on rooftops to find out what the pictured property is valued at.




I like Zillow, but it's incredibly inaccurate for many parts of Chicago. It doesn't seem to play well with multi-unit buildings...
Zillow.com can be helpful, especially with the recent sales info. Like Virginia says, though, I wouldn't put much faith into their price estimates.
Not sure that's it's more nosy than the other stuff that's out there, like Domania, although I think Zillow is 0the first to use Google Maps in this way.
Between the Cook County Assesor's Web site and the Tribune's online database of sold properties, you can find out a good bit of info about just about any property that's been bought or sold in the county in the last 10 years.
I can see my cat from here!