Logging into my router I've pulled this lovely little bandwidth graph that gives a good indication to how much data I'm pushing out.
Before the litter cam I was sending an average of 5GB of data per month upstream. With Ustream I'm now pushing up about 22.5GB a month. This equals about 17.5GB per month broadcasting Ustream 24 hours a day, 7 days a week.
The image sent out is almost always static so I don't know if much more bandwidth would be used with a more animated subject, what with the way digital compression works and all. Eventually I'd also like to try the special Flash encoder that is supposed to push out higher-res video to Ustream viewers, but that will involve a virtual install of Windows which I'm just not looking forward to, to be honest.
The idea of a whole OS running on top of another OS for just one app is unpleasant.