Most of the Linux input subsystem development is being conducted in the main 2.5 BitKeeper kernel. BitKeeper is a very powerful system; although, if you simply want to browse, linus.bkbits.net:8080/linux-2.5 is a useful starting point.
There is a “bleeding edge” development tree solely for the input subsystem, which you can browse at linux-input.bkbits.net:8080/linux-input.
The main development tree for the Linux input subsystem was at linuxconsole.sourceforge.net, but the kernel development has transitioned to BitKeeper. While the site includes little documentation on the input subsystem, there are some useful patches for user-space applications in the CVS tree.
One version of the origin of the AAAABBBB pattern: www.wired.com/wired/5.08/linux_pr.html.