What are you doing up so late? When'll you wake up tomorrow?
If it's the middle/later morning when you read this:
What are you doing up so early? When did you fall asleep last night?
If it's the afternoon when you read this:
Why didn't you go out today? (Or: Why are you on the computer at work today? :P)
If it's early evening when you read this:
How was your day? Did you do what you wanted to do?
If it's later evening when you read this:
When are you going to bed? Why?
As for me, it's early morning, and I'm still talking to friends on AIM. Yay, summer! And I probably won't be up 'till about 11 or 12. Yay, summer!