For people talking about bobbin changes - you can wind a LOT of Aurifil onto a bobbin!
And on some machines, you can adjust how "full" your machine allows a bobbin to get. On my Janome 6600 I was able to move a little teardrop-shaped piece on my bobbin winder so it doesn't kick off the motor until the bobbin is a lot fuller than how it was set up from the factory. Between doing that and using Aurifil, I get a lot of yardage out of a single bobbin.