> moving the > mouse causes the cursor to jump erratically around the screen, almost > exclusively in the vertical direction, along with rio registering button > presses even though I'm not pressing any.
This happens when the usb keyboard/mouse driver misinterprets the HID protocol description in the device configuration. Incidentally this is not specific to 9pi -- Plan 9 uses the same usb device drivers on all platforms. Try forcing the mouse to use the simpler boot protocol, by appending 'kbargs=-b' to the command line in cmdline.txt (on dos partition).
