D'oh! Why didn't I click on them? I've tried it now and it works really well. I have some thoughts on extra features that would make this even better (of course )
One thing I expected though was for double click on the date to both set it and close the pop up, which it didn't.
Just to save a click, would it be possible to have a two month pop-up instead of just one? The example below would make it a lot easier to set longer deadlines, which is going to be relatively often as with a two week assignment, 50% of the time the deadline will be next month.
I also noticed that it is possible to select dates that are in the past. I can't think of many times when that would be necessary (maybe to adjust a previous deadline after a mistake?) but it will normally be an error I think, so a warning/confirmation may be appropriate in this case when the calendar loses focus. What do you think?
Related to this, it would be good to make it impossible to select dates outside of the course start and end dates as per this example: http://developer.yahoo.com/yui/examples/calendar/minmax.html
Thanks for fixing this - it's been bugging me for ages!