Yes I have -- and no looking back.
Initially, due to the nature of the 301 redirect all my hub traffic plummeted as I was systematically de-indexed. Within a week they were all up and ranked again, and the traffic is higher than it was before the change.
So much so that it is back to the way it was before Google slapped Hubpages.
If you are the author of quality hubs, a subdomain change will have an enormously positive effect (because you're no longer lumped in with everyone else in Google's eyes), if not, then you may struggle.
I recommend it.