I would be embarrassed to say how many rulers I have...but I do use them. The only thing I am slowly going from Omnigrid to the Creative Grid rulers. Though I may have all of those I want. I bought the Twister a while back and have not yet used it but really do want to. I love my 8 ½ x 24½ inch, my 6½ x 6½, and my 6½ by 12½....I use these a LOT. I have the 20½ inch square and only use it occasionally, but boy, it does come in handy. Also have the 9½ and 12½ inch squares and use then occasionally.
I think the biggest waste for me was the square in a square ruler. I played with it just a little bit and it has just lain down there ever since.