I initially bought myself an iPad 4, skipping the iPad mini as I deemed it unlikely a good device for my use cases.
Then I played with one in the Apple Store, and my head began to spin.
One really needs to hold the iPad mini to feel how big a difference the thinness and lightness make to usability. I not only enjoy using the iPad mini, but I want to use it everywhere. At work, carrying the iPad mini is like carrying a Moleskine - drastically more convenient.
I initially had three major areas of concern about the iPad mini:
Screen size: I thought the screen would be too small to read documents and mark up presentations. I was wrong on both counts. The iPad mini is a better e-reading device (PDFs included), and marking up documents is no problem either.
Using the on-screen keyboard to take notes in meetings: I have not experienced a dramatic slow-down in speed or deterioration in accuracy typing on the iPad mini keyboard vs. iPad. In fact, I typed this post entirely on the iPad mini.
Lack of retina display: While not ideal, the lack of a retina screen is compensated for by the thinness and lightness of the device. I am sure we will all be blown-away when the retina version does get released, but I am very happy with the current version nonetheless.
Two days ago I returned my iPad 4. The iPad mini is now my main iPad, and I do not expect to go back to the larger form factor any time soon.