Etiquette: Online contacts. If you sign on and see a contact online should you say hello or not?

Would you consider it rude when someone does not say hello? I mean sometimes we are signing on quickly and do what we need to do and get off. So sometimes you don't want to say hello and sometimes you don't want anyone saying hello. However, what is a "hello how are you" right? Aren't we a rush rush society that accepts rudeness as the norm? Shouldn't we stop just to say a quick hello.Yet, if you have alot of contacts you don't want them all writing an IM just to say hello. Imagine 20 IMs! Unsure what is good etiquette on this.