I can only imagine the buying frenzy if the mini was retina! Bottom line is if you go out and try out the ipad mini, it will really change your mind. I can see why it is sold out and let me say that I am 100% content with the ipad mini. The siri is great, the cameras are fantastic, and best of all I can carry it everywhere and use it with ease. The ipad 3/4 is just great but it's not as ideal as an ipad mini when you need to use it everywhere and because of the weight, you can hold it further away from your eyes and that will convince you the display is good enough!
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I agree that once the iPad mini gets a Retina Display it will a truly spectacular device. My first iPad was the 3rd generation, and my first iPhone was the 4S so I'm definitely spoiled by the Retina Display. I notice the blurriness on the current mini, but the size and weight are definite plusses.
I think for now I'll keep my 3rd gen and the mini, but when the mini gets Retina, I'll probably unload both and replace it with that version of the mini. I just can't get over how light and easy to hold it is.