So, just how complex is Google PageRank?

I found this page about how Google sees itself as developing the "perfect search engine" interesting...

PageRank performs an objective measurement of the importance of web pages by solving an equation of more than 500 million variables and 2 billion terms.

Just in passing, I used Google's search engine interface on my mobile phone this past weekend, it's staggeringly fast and surprisingly usable despite not all sites being mobile browser friendly... including this one. Uh oh.