A while ago I designed and then on and off led development of Debian's new installer. It's been quite a successful project.
I wrote a d-i retrospective on the first four years of working on debian-installer in my blog, with some cool graphs.
Its website is formally http://www.debian.org/devel/debian-installer, but http://wiki.debian.org/DebianInstaller is perhaps more interesting.
The dilab was my own rack of d-i test
machines. This ran on
digress, the d-i regression suite, which is the
most obscure part of d-i I know of, and which I wrote.