Poor, poor Visual C++ developer. You see these MinGW or Linux guys using GNU make on their fancy quad core machines to compile Qt. They are already hacking again while you still sip at your coffee, watching the distressing 25% CPU usage in the task manager. And just because nmake doesn't make use of all available processing power.
But good news, everyone! The misery is over. I've writte a nmake clone that can use an arbitrary number of processes concurrently. The thing is called jom and the sources are here, a ZIP with the binary is available for download here.
To install jom, just extract the zip file to a directory which is in your PATH. Now, instead of calling nmake to build Qt, call jom. It automatically detects the number of processor cores in your PC by calling QThread::idealThreadCount(). You also can use the -j command line argument to set the number of concurrent processes.
On a quad core machine with a Qt build takes half of the time it took using nmake. There's still room for improvement. Jom is aimed to be compatible with decent nmake Makefiles. Its not complete yet but hey, you can already speed up your Qt builds!