I'm not sure I'd use it to the extent of the original poster, but I can think of a number of places it could come in handy. Like the ruby(&:function), frequently that is what you want to do.
I would be curious to see if there is any performance hit. I wouldn't think so, but sometimes JS finds a way to surprise me like that.
What a strange idea. It saves a few keystrokes, but at the cost of creating some rather gnarly-looking expressions.