1. Open Dashboard with F12
2. Click the "+" icon in the bottom left (the more dashboard widgets button)
3. Click and drag any widget into the dashboard area - DO NOT RELEASE THE MOUSE BUTTON
4. Press F12 (while still holding the mouse button)
5. Release the mouse button

The widget will now be on your desktop and can be dragged around while alwayys floating over other windows.

Pressing F12 again to access the rest of the dashboard will cause the widget on your desktop to be hidden with all the other widgets when you close the dashboard. And you can't put it back on your desktop unless you drag it from the "more widgets" area. lame.

The steps above to get it to appear on your desktop are from Apple, so it's a supported procedure. The whole widget system is just something that wasn't thought through very carefully though. It's so much an ugly hack with terrible usability.

Bruno