Everybody knows that you can pop up the system clock in Vista by just hovering the mouse over the clock. What you might not know is that you can also do the same thing with the keyboard.
Show the Date: Win+B, Left Arrow
Show the Calendar: Win+B, Left Arrow, Enter
Example:
First, hit Win+B and notice that the cursor is focused on the first icon.
Now hit the Left Arrow key and the cursor will be focused on the clock, which will cause it to pop up.
You can go one step further by hitting the Enter key to pop up the calendar.
Source: howtogeek