I recently had a Solaris failure report from CPAN testers. The failure report had errno.h numbers that I could not interpret, since I lack a Solaris 2.9 box. I knew that Solaris was now open sourced, so I tried to look for errno.h via Google code search. Blech, my google-fu was too weak.
So I instead tried krugle.org. I quickly found the OpenSolaris project, browsed the source code repository and found sys/errno.h. Wow.
It didn't solve my problem (alas, instead I need a new CPAN release with better failure diagnostics) but I was very impressed with the ease of use.
I first learned about Krugle via the 2006 Chicago hackathon. Ken Krugler bought us pizza and talked about getting better Perl/CPAN support into his product.