Don't get me wrong, I 100% agree that sites should be allowed to host their own version of YUI because there are some circumstances where it may be necessary. That's why we distribute all the source code to be able to do it. But also keep in mind this is the Yahoo CDN, if it goes down, all of Yahoo goes down. I can't say the CDN won't ever go down, but to my knowledge, it has never happened.
If you are concerned about CDN reliability, for optimal performance I would still use the Yahoo CDN as you get all the benefits of combo-handling, edge-caching, and (soon) server-side dependency calculation. And as a backup, host on your own CDN in the unlikely event Yahoo's CDN goes down.
We'll look into passing the <C-F> test. :)