One new thing that we have had to deal with is the addition of the CPU_FLAGS_X86 variable to Gentoo and Funtoo Linux. As you may know, there are a lot of USE flags that deal with CPU instruction sets, such as "mmx", "sse", etc. These have been migrated to a CPU_FLAGS_X86 variable, which works similarly to other variables like VIDEO_CARDS.
Strangely, I couldn't find any good documentation on the USE flags that are now CPU_FLAGS_X86, so I created my own docs for everyone on this page:
As you can see, the history of CPU instruction sets for x86 systems has been pretty interesting and complex.
One thing you might be wondering, especially if you are a new user, is what instructions are being used for your Funtoo Linux system. This is actually determined by the CFLAGS -march setting, primarily. This tells the compiler which instruction sets to use when building C programs. The additional CPU_FLAGS_X86 flags enable optional build-time functionality in ebuilds for these instruction sets that must be specifically enabled. Typically, these are special optimized parts that have been hand-written to run very fast on systems with these instruction sets. I hope this clarifies things.
Over the next week, expect updates to the Subarches page on the wiki to reference CPU_FLAGS_X86 instead of USE.