We are succesfully using it from the early stage of the AutoDeploy technology (and virtual Center Appliance as well).
But we are not a big company and we are living (and working) in hungary - thats why the 'big' and 'small' phrase is quiet different
What we really have:
3 site, each with 4~10 stateless ESXi using AutoDeploy.
As I experienced if the deploy rules are working, and you have a good host profile, everithing goes really well. The update process is much more easy and requires much less time to do - even wit this small number of hosts!
I agree that very few conpanies using it right now - but it's not means it is not good to use it