If you're into residential real estate speculation, you're probably familiar with Zillow.com. Zillow.com gives instant and computerized market value figures and electronic appraisals for almost any residential property in the U.S. No more going to several hundred sources to get all the specific information on a house you own (that may be going up for sale) or for prospective houses that you may want to buy and move into or own for investment purposes.

But, how accurate are Zillow.com's estimates? I've used Zillow.com quite extensively and have found the information to be hit-or-miss. It can be way off and right on target. This, unfortunately, makes it very questionable as a resource in my opinion. For example, the county assessor that values most homes in every state is not exactly precise when it comes to judging the actual market value of a home. I believe this is where Zillow.com gets quite a bit of information. Problem is, the estimate can be 15% to 20% off sometimes -- a huge problem.

While Zillow acknowledges that its estimates can be way off in some cases, it cites that the service it provides is only a "starting point" for people trying to figure out how much a home should cost. This makes sense -- and buyers and sellers should use many more resources for reconciling a home's financial worth in every case anyway.