I recently found and activated a "Show IM Online Status Indicator On Topic Page" feature.

Haven't seen it in action yet, but if you IM, keep an eye out for an icon by the author name if you're online.  (Note: you have to fill in the IM field in your profile for it to work.)

There's the culprit; MSN isn't supported, hence the "lightning", but Viper is and AIM I believe.