We let our customers view charges online using the web interface.
I believe it builds trust and I think that our customers are very happy with it (I am not sure how much they actually look at the charges info, they just like the idea they can).
no, we do not let them see charges as this information gets too overwhelming... plus it doesn't give a big enough picture on any specific project or ticket. The clients get all the detailed information they need in their weekly invoices.