WonderMill grinds 1000 lbs wheat - took 9.5 hours
I don't own a WonderMill, but, after watching this youtube video - http://www.youtube.com/watch?v=XmE0Bmid9o4  - where, as an experiment, the mill was used to grind 1000 lbs of wheat without stopping (that's 20 50-lb bags of wheat!) I am left with *NO* qualms about the durability of this mill.
Do take a look at the video - the background music is great.
This was a durability test that we ran on the WonderMill Electric Grain mill. In this test we milled 1,000 pounds of whole wheat continuously for 9.5 hours with out burning up the WonderMill. In fact it was still ready to do more when we ended the test.
========== PS ==========
I have no connection with the youtube posters or the company. Just thought it might interest you home millers out there. Have fun!