Alternative.rb

# I hear that aliasing lambda is bad, but this is
# much more readable...

def this_block(&block)
  block
end

this_block{ @this.destroy }.should change(Thing, :count).by(-1)

Paul's Idea.rb

#Throw this in spec helper
def block_should(matcher, &block)
  block.should matcher
end

def block_should_not(matcher, &block)
  block.should_not matcher
end

#Use it like this
block_should change(Thing, :count).by(-1) do
 @thing.destroy
end

#Which is just a little cleaner version of this
lambda do
  @thing.destroy
end.should change(Thing, :count).by(1)