I'm considering using it because of a combination of the following:
1) You can't always count on users having cached it from the CDN.
2) If it's included on my own server I can be sure they're getting exactly what I intend and there will be less HTTP requests when I include it with the rest of my JS which will only add ~4kb.
3) I'm a bit of a minimalist when it comes to code - for the web at least.