For reasons unbeknownst to the public, with the release of Mac OS X Lion, Apple decided to make dashboard into a space by default. To remove this annoying setting we will follow a few steps.
Here is a screenshot to show you what to uncheck:
Step 1) Open System Preferences (dock icon or spotlight)
Step 2) Click Mission Control in the top row.
Step 3) Uncheck the box labeled “Show dashboard as a space”