(I think this should be posted here and not in the development forum, as this is a complete, working program ... but then, it's pretty developer-centric, so Idonno)
I wanted to make development easier by enabling myself to SSH into the DR800SG and actually have stdout and stderr, and a console. It took an annoying amount of hackery to make it work, so I packaged it up to make it easier for anyone else. The attached binary includes the g_ether gadget ethernet USB driver, and convenience scripts to run them and an SSH server.
A brief howto:
Extract to your SD card. Connect your DR800 and then "eject" it such that it disconnects from the file storage USB connection. Run the app (Programs/usbnet), and it will load the USB ethernet driver, configure itself as 192.168.200.2, and start up the dropbear SSH server. Configure your host to use any other IP on the 192.168.200 subnet, e.g. 192.168.200.1. More info on how to configure the host (Linux only):
http://www.handhelds.org/moin/moin.cgi/UsbNet
To disconnect, exit from the shell presented on the DR800's screen.
In order to SSH in, you will need to configure a root password; by default root has no password, and as such cannot be logged into via SSH, even with keys. You can configure its password on the shell presented on the DR800.
To use scp, you will need to put it in your default $PATH, e.g.:
ln -s /media/mmcblk0p1/Programs/_usbnet/bin/scp /usr/bin/
Before running normal apps, you may need/want to disable the onscreen keyboard which is presented by rxvt. You can do this with erkeyman:
/media/mmcblk0p1/Programs/_usbnet/bin/erkeyman off
A note: USB networking and 3G networking are not friends. I found that I have to reboot the system after connecting to usbnet in order to connect to 3G. This is probably (in fact, almost certainly) a problem I caused, so I'll look into fixing it, but for the moment just keep in mind that you'll have to reboot.
I hope other devs benefit from this. Enjoy!