Traditionally the Mesa DRI drivers have statically linked all of the common Mesa code into each driver build. Statically copying all of this shared code into each of the modules obviously results in larger module sizes and more code that needs to be compiled. With this shared DRI core patch by Intel's Eric Anholt, a shared DRI core library is created instead, which are then dynamically linked to by the drivers.
This saves 30MB on disc (just 4.4% of the working tree size) for my compile of swrast,i915,i965, but as a result reduced my build time for "touch src/mesa/main/context.c; make" by 13.8% +/- 3.8% (n=5). I don't even care about distros, I want shorter build times for myself :)
This shared core is only supported when being built with GCC and for those wanting to build the Mesa DRI drivers with all of the common code statically linked in, don't use the --enable-shared-dricore option. For everyone else there is huge savings in disc size and a faster Mesa build process. See more on the Mesa mailing list.