The throttling isn’t based on how many movies are in your queue, but the rate at which you rent movies. They give priority to people who rent fewer discs per month.
We get 2-3 day turnaround from Netflix for discs, and we’re using the streaming feature more and more. Sometimes on Saturday night we see a streaming movie lock up, and it’s really annoying, but that hasn’t happened any other time. I’ll be glad when they get subtitles for the streaming content, too.