Google:

"Google is providing a selection of about 900,000 web pages in pre-parsed and raw format, together with a "ripper" program that provides a framework for processing the pre-parsed data. Your mission is to write a program [...] that does something interesting with the data, in such a way that it would scale to a web-sized collection of documents. Part of your job is to convince us of why your program is interesting and why it will scale; other than that, you're free to implement whatever strikes your fancy."

I'd like to see something similar to blogdex's Social Network rolled-out googlewide. Since Google doesn't let you mix advanced criteria, I'd like an option to see sites that share incoming and outgoing links (eg. "show all sites that are linked from thissite.com and link to thatsite.com").