I did an Image processing analysis of my symmetrical drawings on MS Paint (by writing an image processing application in C++ ofcourse) using the IPL98 library. I did a statistical analysis for 12 ambigrams (which is a small sample space). You can see some of them on my Ambigrams link.
Surprisingly, I didn't get any result to be a perfect one (that means an ambigram). All the pictures had some error which is quite practical as I was analyzing on the basis of pixels and all the pictures have been hand drawn. The average percentage error which I got is 16.3467 which is quite high.
I think I still have to go a long long way to get that perfection.
[Please Note: There is a bug in the compilation of the IPL98 Library. If you download it and try to compile it, it would give an error in one of the classes. I tried to report the bug, but I didn't get any response. I solved it though. ;)]