Does Anyone Specialize in Vacant Properties as a Source for Flipping?

[Chris Roy]

I have experience with renovations and rental properties and am considering getting into flipping properties.  One area I have looked, at as a source of properties, is vacant and condemned properties.  I have noticed that some cities have public lists of these properties.  I have also noticed that some cities are very willing to help get these properties usable again.  

Does anyone have experience with vacant and/or condemned properties as a good source of properties for flipping?  Is this a good source of finding properties, or would I be wasting my time?