Interesting post from Google, in which they say:

"Recently, even our search engineers stopped in awe about just how big the web is these days -- when our systems that process links on the web to find new content hit a milestone: 1 trillion (as in 1,000,000,000,000) unique URLs on the web at once!"

Puts CrossRef's 32,639,020 unique DOIs into some kind of perspective: 0.0033%. But nonetheless that trace percentage still seems to me to be reasonably large, especially in view of it forming a persistent and curated set.

Update: Talking of Google numbers, pingdom has a post "Map of all Google data center locations" with maps of US, Europe and World locations.