It's quite easy, actually...
1) Check if it's Saturday or Sunday
2) Check if it's a Holiday
3) Check in my "days off" file to see if there's an entry for this day
4) Check what time it is
Et voilá! I can see automatically discover whether I'm working or not and have a different configuration deppending on that!
Now... you wouldn't happen to know how to run a command in a specific workspace, would you? (running Gnome, here)