When going into my instant messaging or Second Life and notice that someone else is already online, who has the ultimate responsibility to take notice? The person signing on or the person already there?
Thank you for your question, my friend. In this new era of continuous, instant multiple channels of communication, these matters of IM/chat ettiquete (chattiquete?) are familiar to us all. This is an excellent example. I would say that a lot depends on the circumstances and the nature of the relationship. It would certainly be impractical to suggest that we all have an obligation to ping everyone on our contacts lists who happens to already be on when we log in. That can swiftly become rediculously overwhelming for all concerned. If, however, the person in question was expecting you for a pre-arranged rendezvous or it is someone with whom you regularly spend most of your online time, then giving them an IM wave is reasonable.
One should consider that the other party is likely engaged in some other activity rather than simply staring at the contacts list waiting for you to appear (although this may be the case in some relationships). If they are in fact so engaged then it is quite easy to miss the "Bob is online" popup. This is particularly the case in SL when using Viewer 2. In this tiger's opinion, the popups have been made considerably less noticeable in Viewer 2 when compared to earlier versions.
In general then, I would put the resposibility of first contact on the one who has just arrived rather than the one already there. It is analogus to entering a crowded room and waiting to be noticed. It is much more effective to walk up to the person for whom you are looking and tap them on the shoulder.