|Wow!!! Thats large. We use to run a picture of the week contest and I had a huge one that I started the series with - it looked like it was as old as the tree it was growing on which was probably 70-80 years. Can't find it now but it was about 6" in diameter if memory serves and had some pretty scary looking poison ivy vines. :-)
I did find this one from someone else in our uploads area...
It sounds like yours is a little bigger than this one. Would love to know also what others have seen.