df should work from outside the chroot.. when you're inside, because of mtab being copied over, the mount points don't match up fully, so it gets confused.
As for using Debian as the main OS, you can already do that... just create a bootable SD card with Debian on it, with all the right drivers and everything which you could copy from your Angstrom install. If you want to install it over your NAND however, that could be a bit of a more interesting experiment to try.
In reference to Android buggery in a chroot, it's really not going to work right at all.
Just to add more flames on the fire in a certain General thread ( I may cross-post this there as well, ) Android is Linux with "other bits," where these other bits cause issues.
The reason that this chroot hackery works is that most Linux distros follow a few guidelines.
They mostly all use the same system hierarchy for the most part ( though some have the habit of going their own way in places. )
And they generally use the same kernel, though sometimes with little patches.
Android doesn't follow either of those two, which are the most critical in getting a chroot to work.
Android's kernel is a rather modified Linux kernel, where their changes have already been revoked from the main tree due to stagnated updates. Nice. ( see: http://www.h-online.com/open/news/item/Android-code-removed-from-Linux-kernel-920688.html ) And their root filesystem is "a bit weird" too. /dev /sys and /proc are where you'd expect, but that's about it.. everything else linux-y tends to live under /system .. and due to their kernel changes, will do nothing but segfault if you try to run them either directly on the Pandora, or as a chroot argument.
If you're wanting to run Android alongside Angstrom, I see a more VM-based environment working, and considering it comes with one in the SDK, I'm surprised no-one's recompiled that on the Pandora yet...
However, I do seem to be spreading myself a bit thin again, so for the time being, I won't be looking at it.
I still have to get out these Compressed Debian extends! I keep forgetting and mangling them while looking at x86 or Android code
So I shall be setting up a Compressed Debian extend with enough to run Synaptic today, and that'll be that for a while ( save bug fixing and support ), as I've other projects ( which for me, are more fun at the moment ) that are wasting away!