2/20/2008 - no2chem has finally cracked the code and came up with a better, permanent solution for killing the service LED here -
http://forum.ppcgeeks.com/showthread.php?t=18871
He now has an app called nueLED that will allow you to enable, disable or redirect LED functions for any of the LEDs (bluetooth, charging, service LED etc). More improvements to come.
NOTE: no2chem's nueLED should work with any HTC device and possibly other WM phones. My older LED Killer should work fine with phones other than the 6800 if you happen be unlucky enough to have a model of phone nueLED doesn't work with.
If nueLED will work with your device then use it over LED Killer as his method is so much cleaner, has more features and uses less system resources.