Hmmm. I never had my phone shut down or reboot in correlation between g_ether and/or plugging it in. If you can find another computer, you could try it with that one, and see if it reboots upon loading g_ether and connecting to that computer too...

It could honestly be either the computer or the N900, or some combination of stuff on both ends.

Did you run the ifup usb0 command before loading g_ether or plugging it in by any chance? What I would do first off is run "ifdown usb0" as root before loading g_ether or plugging it in.

It could also be a bad Mad Developer installation, in which case if you can reinstall it, that might help.

Beyond that, I would compare the list of everything we have installed on our devices, to see if there's anything we can find through process of elimination that might be causing the reboot for you.

(Also, I just remembered, I find that I cannot get USB-internet to the N900 if I have FreeSSHd running on my Windows Vista machine. I haven't bothered looking into it, but I have FreeSSHd installed on my windows laptop, and whenever I have it running and loaded as a server, it interferes with Window's internet sharing. Do you have any servers - or clients, for that matter - constantly running on your computer when you try to connect? FTP, SHH, Telnet, whatever-else-exists?)