Sorry for the geeky title, but if this post applies to you, well, you’ll know exactly what it means.
If you’ve ever poked around in the power settings of Windows 7, you’ve probably seen a check box that lets you specify whether Windows should be allowed to wake up when another network device sends it a directed packet.
Today I stumbled across an apparently definitive answer in the Readme file for an Intel network driver:
Power Management and System Wake
Not all systems support every wake setting. There may be BIOS or Operating System settings that need to be enabled for your system to wake up. In particular, this is true for Wake from S5 (also referred to as Wake from power off). Microsoft Windows 7 and Windows Server 2008 R2 do not support on directed packet. Systems with these operating systems will not wake on a ping or other directed packet.
System does not wake when expected
Under Microsoft Windows 7 or Windows Server 2008 R2, the system may not wake when sent an ARP packet. Forcing your system into Home Networking mode (instead of work or public mode) will resolve the issue. You can set the network mode during install or from the Networking Control Panel. However, if the network is disconnected and reconnected, and a DHCP server is not available or if there is no default gateway defined, it appears to the operating system that the network is undefined and the OS will reset it to public.
System does not wake on link
On a driver-only installation, if you change ‘Wake on Link Settings’ to Forced and change ‘Wake on Magic Packet’ and ‘Wake on Pattern’ to Disabled, the system may not wake up when expected. In order to "Wake on Link" successfully, check the Power Management tab and make sure that "Allow this device to wake the computer" is checked.
This information is especially useful if you have a Windows Media Center or a shared media library on a Windows 7 PC that you want to access from a networked device, such as an Xbox 360.
If you have tinkered with these settings, successfully, or unsuccessfully, I’d be interested in hearing about your experiences.
Ed Bott (@ wordpress.com) 
Geek away! This was very helpful. Thanks!
My wife’s PC used to be able to Wake On Lan when it was running Vista. When I upgrade it to Windows 7, it would no longer wake up. I upgrade the BIOS and the network card drivers, but was never able to reactivate the functionality.
I have gotten WoL to work on my home laptop behind your typical home router setup. However, what many users have a problem concerning WoL is consistency. WoL would work one minute and then after a few minutes of inactivty, it wouldn’t work due to routers flushing out the ARP cache. It’s weird because I thought I had this problem ironed out by using static IP and port forwarding. It worked for a time but once again, it just stopped working one day. Very weird. I am on Windows 7.
In a time where cutting energy cost and going green is so dominant, there has to be a better method for users to utilize WoL technology. Is there even a native method to send a specially crafted WoL packet within Windows? Almost everywhere I ‘ve read that you have to use third party services or utilities to send these packets to wake a computer.
I have not seen this in the Power Settings. I guess it only shows up if your computer supports it?