I used it rather extensively to model a dress form. It does best job of determining the shape of the objects accurately when it has a lot of features to match from different angles. The dress form, for example did not; so we had to place reference marks on it and manually assign as many points as possible.
But after doing this, I had a pretty darn good base triangular mesh that I was able to work with in Meshlab (and Blender, and Maya, and Rhino) and I had it REALLY QUICKLY.
The project we used it for has been stalled for a while and we haven't output anything based on the model. So I can't tell you how accurately it scales to the real world. Even if the coordinate system internal to 123D Catch is robust, the (rather elementary) UI does not feature coordinates beyond maybe a ruler. So it's at least good at providing a base shape, if not a perfectly determined one.
All in all: it's free - or was as a beta at least... it is surprisingly powerful, and if you need to use it manually, the interface is elementary. And once you start working "within" the program and understanding how to get good results, 123D Catch is pretty stunning.