Several people have suggested that you add the capability of setting an hourly rate for an account rather than a technician. I think adding an hourly rate as part of an SLA might make more sense in the context of SC.
Also, for future releases it might be helpful to make SLA's more flexible, i.e. an SLA could be set up for ad-hoc clients (those who get a bill each time a request is handled), prepaid block (clients who purchase some number of service hours to be used over time), and perhaps a monthly type where the client receives X number of hours service per month.
Then based on the SLA, reports could be created showing various things, like how many hours a prepaid block client has 'left' (maybe this could be incorporated into the customer portal?). Adding the 'time spent' field for a request (with a total) in the client view might be useful as well.
Overall, I think this is a great product and can only get better!