Google doesn't usually go down, but routing issues or DNS problems mean that it does happen that they are unreachable.

How often are there routing issues to Google, but none to your site? It's much more likely that your site will be unreachable. The probability that Google will be down is probably insignificant for most cases.

I have several times been unable to reach Google but have been able to reach my own site.

It did not happen for very long (a few minutes each time), and not often, but it has happened.

Last week I found an issue with routing internal to Yahoo's core network that was causing an esoteric DNS failure for our customers.

Routers are configured by people, and people make mistakes.

Yes, but what does that have to do with Google's reliability? What does it have to do with routing issues between one particular site and Google?

He's not claiming that Google is infallible. I'm more confident in their ability to maintain availability than yours. All of this paranoia about Google going down is mostly FUD.

Well, depending on multiple sites for critical data of course multiplies the risk of failure. But the risk of depending on one other highly reliable site for something that should almost always be cached anyway is indeed very very small.

I wouldn't say this whole issue is FUD though. For instance I would not want to depend on four different even high quality third party sites for each request to my website because the likelyhood of failure would be (almost) five times as high.

You missed the point, which was that your site could be up, and google would be down, which would cause big problems with javascript errors.

OTOH if your site is down, it's fully down - no partial content, and javascript errors.

I understand your point and I'm dismissing it as FUD because you're playing the "what if" game. Comeback with some uptime graphs. I don't believe it's worthwhile to worry about Google's uptime and it's perfectly legitimate to let them host jQuery for you until proven otherwise.