For strangers use something like the above.
For acquaintances either use the above or make a one sentence comment about a single issue and how you feel about it but avoid anything overly personal unless you know its safe, for example:
Quote:
"How are you?"
"Stressed out, too much coursework"
And don't' feel constrained by the exact literal question:
Quote:
"What's up"
"Stressed out, too much coursework"
is equally valid. With acquaintances chances are you're in the same something: same school / university / office: while you don't have to respond with anything related to your shared situation, its a safe topic.
After you've responded either leave the air open for a very brief expression of congratulations or sympathy* and then ask the same question of them or just go straight to asking the question. If you don't have anything to say fall back to the answers people mentioned above.
With friends you need not feel constrained by the rules of the ritual, I for example have occasionally responded to this question on instant messengers by pretending I'm out and its my computer talking. Follow the rules for acquaintances unless you have something better to say.
* If you have a serious problem that you think deserves more than a brief expression of sympathy you probobly shouldn't be bringing it up to acquaintances, that's what friends are for. The exception is if you think the acquaintance is qualified to help in a way that friends can't, if that's the case then you should deliberately break the ritual's format, for example:
Quote:
"What's up"
"thank goodness I found you"
...