YUI admitted today what has actually been the case for quite some time: YUI is dead. I always remember seeing YUI as a curiosity when everyone was gushing over jQuery, but in a lot of ways they were ahead of their time in promoting things like modularity.
Cheers YUI, even though I never used you, I can tell that some smart people worked hard on real problems in a way that paved the way for the rich JS ecosystem emerging today.