The highlights for the PowerPC architecture with the forthcoming Linux 3.9 kernel include a hand-tuned SHA1 implementation written in Assembly for PPC, support for doorbell interrupts on POWER8 (they're a kind of fast thread-thread IPIs), support for saving/restoring and context switching with the Processor Priority Register (PPR), DAWR watch-point facility on POWER8, support for changing the Data Stream Control Register, support for context switching the TAR register on POWER8, improved preservation of the CFAR register, and support for Transactional Memory on POWER8.
As one can see, most of the PowerPC work queued up for Linux 3.9 is about POWER8, the latest-generation of the PowerPC architecture. IBM is still developing POWER8 and it offers improved simultaneous multi-threading (SMT), greater reliability, larger cache sizes, new accelerators, and a greater number of cores. POWER8 processors will begin appearing in late 2013 or early 2014. IBM POWER8 support first appeared in Linux 3.8.
The pull request for the PowerPC updates to go into Linux 3.9 were sent in on Saturday and can be viewed on the Indiana kernel mailing list.