Last week I tried to show my boarding pass to a Delta gate agent for check in and was told that the reader often has problems reading anything other than an iPhone size screen. He printed out a paper boarding pass for me. YMMV
I've just come back from a trip last week and I saw a couple of people just present their iPads at the boarding gates. I would check to make sure that your particular airline will accept this though. Not sure how they saved it, but I have just taken a screen print of other vouchers and presented them in stores on my iPad and they were accepted.