I've searched and read extensively in this forum. It may be drop dead obvious to everyone else on the planet, but just to be clear, let's go over this one more time (starting with a SheevaPlug running the v1.1 set of downloadable components).
1. Upgrading u-boot using "bubt uboot.bin" whacks the RFS on the nand flash. Right? Subsequent attempts to go back to booting from nand have the kernel wailing about a blank flash. Right?
2. The stock kernel (18.104.22.168) doesn't support the RFS on SD, does it? U-boot upgrades are NECESSARY but not SUFFICIENT to overcome the refusal of the system to find the RFS on SD. Right?
3. Other people struggle with the much-vaunted "Installer" when running from Windows, right? Other people find the Installer instructions...somewhat lacking, right?