I installed qemu a few days ago on my Windows laptop to test how fast it is and whether it is able to emulate an X server so that it is actually usable. The result is surprisingly positive. I installed Gentoo Linux on it, so it did hardly anything else than compiling a packet after the other since I set it up. I think this is the first time, the dual core processor in the notebook is of real use: While qemu only emulates one processor for the virtual machine (although it could emulate both, I believe), the other one remains for the rest of the system and so my other applications run without any noticeable delay.
I always wanted to be able to do some gnome development when I am not at home, but I do not want to install Linux on a separate partition because the hard disk capacity is "only" 60GB and I had some space problems on Windows on the last laptop. It also annoys me that I have to reboot every time I want to switch from Windows to Linux or vice versa. On the other side, I do not want to remove Windows from the machine either (well, I probably want, but it is not an option) because there are some applications like Evernote that exist only on Windows and since Gobby is officially supported on Windows anyway, I should be able to provide Windows builds and perform some testing.
To summarize, the qemu approach seems promising and I look forward to work with both operating systems without having to reboot all the time. Currently, the Gentoo is still compiling Gnome (36 out of 215 packets done). 