I stick a random delay between downloads, never download streams in parallel, and always download when nobody is using YouTube (ideally when nobody is home or everybody is asleep).

I never did get throttled-- I just stuck in "you must login" hell. We don't login to YouTube in our household, so that effectively cut of my wife and daughter. My wife couldn't have cared less but I learned that being able to stream music videos while getting ready for the day or bed is mission-critical for my daughter. (I've asked her to identify channels I can sic the archiving rig on but, heretofore, she hasn't done it. I keep telling her those videos she likes could disappear at a moment's notice...)