The most relevant net resources are:
http://penguinppc.org/usr/embedded/
Introductory stuff.
The MontaVista FTP site is a good starting point.
http://lists.linuxppc.org/lists/linuxppc-embedded
The archive contains indispensable wisdom answering most of your questions before you knew you needed to ask them. Browse it heavily.
In particular, look for any articles by the individual gurus mentioned in the Credits. Unfortunately you can't search the archives by
From:line to do this yet.
You are encouraged to subscribe by visiting http://lists.linuxppc.org/listarcs/linuxppc-embedded/info.html. However, please search the archives before asking questions.
Instructions like "Search for ..." in this document refer directly to the search engine at the mailing list archives for the specified keyword. Follow the keyword link to perform the search.
The ABI and EABI documentation describing register usage and C linkage conventions are available at: http://www.esofta.com/softspecs.html
There is lots of invaluable information about optimisations for the PowerPC architecture in the IBM PowerPC Compiler Writer's Guide at: http://www.chips.ibm.com/techlib/products/powerpc/manuals/compiler/cover.html
PowerPC technical discussion.
General discussion of all flavours of embedded Linux.
General embedded system discussion.
Leif Lindholm's in-depth report on porting Linux 2.2 to a custom MPC860 platform: http://www.realtimelogic.com/staff/leif/linux/linux_860_report.pdf.gz
Matt Porter's Linux page: http://members.home.net/mmporter/linux/
LinuxPPC Solutions offered by DENX Software Engineering: http://www.denx.de/solutions-en.html