We use Throttlebox and it's amazing. It's cut down on the people who join for a trial and download everything and then quit, and has also improved overall access to the site by managing bandwidth.

Took a little while to get it tweaked to the point that it was reasonable so members didn't bitch, and we got a few complaints until we made a custom error page that pops up when people exceed their bandwidth allocation. It explains why we manage bandwidth, what they can do to fairly use the site and avoid the errors, and gives a link if they want to comment about it. Since the error messages, I think we've gotten maybe two complaints total.

It also gives great reporting so if someone claims they didn't have access to the site and asks for a refund, you can run a report of every video and still image they've viewed. I've defused several bogus refund requests that way.