Pretty nice and it usually "just works". Recently, KDE has switched over to it, and since then I also gave it a try and I must admit so far, it's the best build tool I tried. Aqsis is also using it and it works pretty well so far; supporting Mac OS, Windows and Linux -- this is where I had my first personal contact with CMake.
CMake 2.6 has been released. See the release announcement. CMake is a very nice cross-platform build tool which does not build itself but instead creates projects for the target platform (Visual Studio projects files for Windows, Makefiles for Linux, etc.).