There are quite a few devices out there that are capable of dual booting. Now it seems that the ZTE Blade has also joined that club thanks to XDA Forum Member android@sam. This project is still at a very early stage, and is currently only compatible with one particular CM9 ROM. However, it demonstrates that dual booting is indeed possible on this device.
The developer plans to extend the project to support as many of the ROMs currently available for the device as possible. In the developer’s own words:
This mod works on the basis of two scripts which are to be executed in the terminal emulator or script manager and a modified boot.img to boot the rom from sdcard instead of NAND.
The process involves quite a few steps, including partitioning your SD card and replacing the boot.img of the ROM, but all of these are covered in the original forum thread and you should be up and running in no time. If you would like to test this out, head over to the original thread.