I can't find any mention of this, but Stack Overflow is unusable if ajax.googleapis.com is not available. I know for many people Google's availability is not usually in question, but I noticed it when testing for a large corperate client of ours, who literally do block googleapis.com for their staff. It's also an issue in countries like Iran where Google is blocked, or on the off-chance that just googleapis.com goes down (not likely, but still possible).
The work around for this is very simple: Best way to use Google's hosted jQuery, but fall back to my hosted library on Google fail
Is there any reason this is not done on SO?
I just found someone did ask this last year, so this is a duplicate: