In the day and a half that I've had the mini, I see it more of a COMPLEMENT to the iPad3 rather than a replacement.
So far, I can't see myself getting rid of the iPad3 simply because of the bigger size and retina display. When I first used the mini, the text didn't seem too bad, especially when reading in landscape. However, last night while reading/surfing for an hour or so, the text on screen really started to wear on my eyes.
After a while, you really start to notice how bad the text is in portrait orientation, even with the mini a normal distance from your eye (worse, of course, if you're holding it relatively close).
So, for now, I'm keeping the iPad3 and complementing with the Mini. If the 3 gets little to no use the next few weeks, it will likely be sold to fund a MBA