I've always wondered why Macs could wakeup from sleep by a mere keystroke, but my Linux boxes required me to press the power button. It turns out you can enable wake from suspend/hibernate in Linux by adding the following to /etc/rc.local, which is run at startup:

for i in `/bin/grep USB /proc/acpi/wakeup | /usr/bin/awk '{print $1}'`; 
do 
    echo $i > /proc/acpi/wakeup; 
done

/proc/acpi/wakeup will then look something like:

and voila: when your Linux box suspends, you can wake it up by pressing any key on your USB keyboard.