Okay. This looks very cool and I've tried a few things but still seem to be missing something.

First, I've followed the instructions from Matan (more or less) to use his kernel.

Things I am doing differently:

First, before I load it permanently, I want to try and get things a little more configured the way I want, so I'm flashing from my Linux box:

sudo flasher-3.5 -k my.u-boot.power41d -l -b

My N900 starts uBoot and if I interrupt it and do a run noloboot I get taken to my regular boot process (which runs Multiboot giving me the choice between Maemo and NitDroid)

However, I have 16G SD card. I have Nitdroid at mmcblk1p7 and MeeGo at mmcblk1p5. (See MeeGo Bug 5136 for a discussion of how I did this).

With that, I've been trying to find ways to get bootargs environment to pass, e.g. root=/dev/mmcblk0p5.

I've installed my uImage in the first partition of my external mmc card. Then I try
mmc init
fat2load mmc 1:1 ${loadaddr} uImage
setenv bootargs root=/dev/mmcblk0p5
bootm ${loadaddr}

This through the startup, but it gags on the filesystem with essentially the same errors as I described in comment 9 on MeeGo bug 5136.
complaining about mmcblk0p5.

Anyone have any ideas?