EDIT: From now on, the latest versions of the files will be kept in the feature request: http://code.google.com/p/libhsplasma/issues/detail?id=8
I've created a CMake buildsystem for libPlasma and the tools. CMake is a meta-buildsystem that can create Makefiles, XCode projects, Visual Studio projects, and a number of other buildsystems. Using it means you only have to edit source lists and such in one place and all the platform-specific builds "just work".
I've tested it on windows using mingw (already a platform not supported with the old build method!), and on 64-bit Linux. It seems to work - everything builds and links. 'make install' is all set. Source grouping in visual studio is possible (and the sources are already 'grouped' into different variables in the CMake file), but I haven't implemented it yet.
The CMake files for libPlasma are at http://stashbox.org/803314/PlasmaCmake.zip
The CMake files for PlasmaShop are at http://stashbox.org/798116/PlasmaShopCmake.zip
EDIT: Remembered Stashbox, and added a few more details about what's implemented
EDIT2: Update with header file installation and CMake files for PlasmaShop &co
EDIT3: Updated for libPlasma r370