if you have too many gadgets to display, some will be hidden. move your mouse to the top of the sidebar area and click the right/left arrow to scroll the gadget list. if you've removed the gadget, click the + sign to add it.
p.s.: imho, the sidebar is a resource hog. google desktop's sidebar is better alternative.
I've lost my notes stored on the standard gadget.
Any one know how to retrieve them ?