It seems now that this problem is not isolated case as it happened to me,
I solved this problem using the 3rd party application "setting profiles". i think this a paid app on the market but there is a lite version that you can use.
first, u need to create an profile, in the profile, which is the majority of the phone setting. mark the star and tick on the "pulse notification light". then activate the profile that you have created. then test your notification LED,
by sending sms to yourself then put the phone to sleep. like what i have said, notification LED works only when the phone is in sleep unlike before in 1.6. when you receive the message, about 4 sec delay, the notification LED should be lighting up.
afterward you can uninstall setting profile app.
i hope this solves your problem.