I've already spent a few hours to finally get this working again. There are several problems in Ubuntu 8.10 considering Wake on LAN:
1. The network cards' drivers are unloaded during suspend.
This often deactivates your card's wake on lan feature and completely powers it off.
You have to add your network cards driver module to the MODULES_WHITELIST in /etc/default/acpi-support. Also add the network card's interface(e.g. eth0) to SKIP_INTERFACES.
2. The network is not (properly) restarted after resume.
a. NetworkManager overrides settings in /etc/network/interfaces.
The easy way is to simply remove networkmanager: sudo aptitude remove network-manager.
b. The network setup script is not restarted after resume.
You can add the script (networking) to STOP_SERVICES in /etc/default/acpi-support.
3. Wake on Lan is not enabled by default
You need to issue e.g. sudo ethtool -s eth0 wol g. You can do that in an init script and you will likely have to do it again after resume. (I've put it a script to do that into both /etc/acpi/suspend.d/54-wol.sh and /etc/acpi/resume.d/99-wol.sh )