Hi Lars,

>I'd like to try if a system here can use Wake-On-LAN to recover from
>suspend or even cold boot after getting turned off. I've enabled Wake
>On PME and Wake on Modem Ring in the "BIOS"
>
>Is that enough, and if so then what is needed on the software side?

Install "ethtool". The package has some ifupdown hooks besides the tool itself.
In your interfaces file, add "ethernet-wol g" or similar to your interface
options. See the ethtool manpage for the possible parameters to the "wol"
option, "g" is for reacting to the standard WoL magic packet.

After an ifdown/ifup, run "ethtool <iface>" as root, you should see something 
like this in the output:
    Supports Wake-on: pumbg
    Wake-on: g

HTH,
Lehel