In OS X Mountain Lion I don't really know how I can delete a widget from dashboard. It should be simple, but seems like it OS X Lion were more simpler than Mountain Lion, because you need other's help doing something in the OS X.
Thanks for the help!
It is simple.
go to Dashboard, click on the ⊖ sign. All the widgets will get a small ˟ badge on the left. Click on the ˟ and the widget would be gone
Or click the ⊕ sign. In the resulting screen showing the widget collection, click the ⊖ sign to again get the ˟ badge on the left for each widget. Click to delete. You may get some confirmation messages.
also you can only remove user added widgets and not the system included ones (as far as i know)