I'm researching the D945GCCR intel motherboard, and the manual says this:
For LAN wake capabilities, the +5 V standby line for the power supply must be capable of providing adequate +5 V standby current. Failure to provide adequate standby current when implementing LAN wake capabilities can damage the power supply.
I just did a search on this subject: "+5 V standby current power supply", but actually a better search term is "5VSB":
ATX Power Supply Power-On Switch - this page is actually very helpful! It explains how the power on switch works.
Finally found the wikipedia page on power supplies, which had these helpful tables:
|+3.3 V||1||13||+3.3 V sense|
|+3.3 V||2||14||-12 V|
|+5 V||4||16||Power on|
|Power good||8||20||-5 V|
|+5 V standby||9||21||+5 V|
|+12 V||10||22||+5 V|
|+12 V||11||23||+5 V|
Also found this interesting but unrelated page: