Opinions on time banks?
So I was reading Kevin Carson's Desktop Regulatory State, and I got to the part where he talked about networked currencies and time banks to organize barter networks.
It seems like a good idea, but I wanted to know if there were any anarchist (preferably mutualist) critiques of time banks? I know money is a controversial subject in anarchism in general, but are there any specific limitations of time banks or credit-based currency that I should know about?