This is just a small collection of links, describing how to setup Multiboot on the Motorola Defy.
- [DEV][2012/04/13] Multiboot v0.5.5 - xda-developers
- [DEV] [APP] [14/04/2012] Multi Boot Manager 1.42a (TWRP support)[Translators needed] - xda-developers
- [ICS][CM9] Defy/Defy+ [Froyo kernel: 16/05 Epsylon3][GB kernel: 16/05 Epsylon3] - xda-developers
To install a system on a VFS, reboot the phone and select Recovery(CWM) in the Multiboot menu. The update.zip can then be flashed as usual.
I did install a Cyanogenmod 9 Nightly using Multiboot on my Defy. The performance is not as good as a CM 7.2 that resides on the NAND. The reaction to button-presses is lagging quite a bit. This may either be a problem with the linux kernel (I am using a rather old one) or the fact, that the VFS is stored on the SD-Card.