A very interesting article about how DRY you should be in your specs.  

http://lindsaar.net/2008/6/24/tip-24-being-clever-in-specs-is-for-dummies

Personally I agree with everything said.  Readability comes first, even at the expense of efficiency and DRY; “be nice to those who have to maintain the code”.  The really interesting thing though is the example is actually quite DRY - it’s more about how you organise and order the code, more than repeating yourself.