I was browsing the NEWS file after building up version 23.1 and read that support for Solaris 2.6 will be removed in a future version of Emacs. A few of my coworkers and I are still regularly using Emacs built on a Solaris 2.6 system. If I couldn't upgrade past version 23, I guess that wouldn't be the end of the world, but it would be nice if the capability was maintained.