Who's Online is pretty cool for checking on what everyone's doing at a given moment. Anybody notice that members tend to be reading mainly current threads, while Guests delve into the archives a lot more? I've found a lot of interesting old threads by stalking Guests around
Myself, I don't particularly mind people seeing who I'm PMing, but it makes me a bit uncomfortable to see Person X PMing Person Y, like I'm watching some strange little love affair I'm not supposed to know about...