I'm using the weather gadget on my desktop, and today out of the blue it disappeared!
but not completely, there's a
(i) icon there and you can see the close button (X) when you move the mouse over it...
How can I get it back?
Try going to control panel in category view (in the top right you can set the view). Click on appearance and personalization once under the category select: "restore desktop gadgets installed with Windows". This seems like the easiest option for fixing this.
This fix seems to have worked, all credit to Shawn on the Windows 7 forums.
Several times when I've lost my gadgets I use the desktop context menu View -> Show Desktop Gadgets two times, uncheck it and then check it again. After a startup pause they all come back.