I haven't been able to get it to wakeup on GPIO0.  I think it probably in the mux settings.  I'm not using an LCD so I'm using GPIO 114 instead and that works fine.  You have to enable the GPIO pin as a wakeup source in board-overo.c .
What kernel version are you using? 

From: coderdrone@gmail.com [mailto:coderdrone@gmail.com]
Sent: Thursday, March 18, 2010 1:13 PM
To: General mailing list for gumstix users.
Subject: [Gumstix-users] Gumstix Overo Won't Stay in Sleep Mode


I have recently been looking into power management on the Gumstix Overo Earth.  From what I've read, you can 'echo mem > /sys/power/state' on the commandline to put the system to sleep.  This seems to work.  However, the system immediately wakes up.  I've tried this both on the Desktop image that shipped with the Gumstix, and a console image that was built on an SD card.  In both cases, I'm running the 'echo mem...' command through the USB console port.  How can I get the system to stay asleep?  Also, once it stays asleep, as I understand it, GPIO0 can be used to wake it up.  Would that just involve shorting GPIO0 (pin 13 on the 40-pin header) to a 1.8v line (pin 16 on the 40-pin) to wake the system up?

Here is the output when I try to enter sleep:

root@overo:/sys/power# echo mem > state
PM: Syncing filesystems ... done.
Freezing user space processes ... (elapsed 0.00 seconds) done.
Freezing remaining freezable tasks ... (elapsed 0.00 seconds) done.
Suspending console(s) (use no_console_suspend to debug)
Class driver suspend failed for cpu0
Restarting tasks ... <7>hub 1-0:1.0: state 7 ports 1 chg 0000 evt 0000
mmc0: mmc_rescan - card ocr from io_op=0x00000000, err = -110

No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.791 / Virus Database: 271.1.1/2754 - Release Date: 03/18/10 03:33:00