Chatting to say good-bye

I like the customer service 'live' chats which many websites offer. For the most part I've found them speedy and helpful. But then comes the awkward moment: how do you say good-bye? In other words, after all the thank-yous and I-sees, where do you just quit?

I don't want to be rude and click the Close button too soon and have them mark my account as ungrateful. I shouldn't switch to talk about the weather because then I'm taking up someone else's time. Eventually the conversation is just over and a good customer service rep will let you know that it's time to let go and answer the survey which will pop up next.

Now if I can just incorporate this into my personal iChats. Saying good-bye in a timely manner, not the survey.