I went to the Apple Store in Legacy Place the day after launch day to check out the newest tablet in town. The same weekend (actually on launch day), I received my iPad 4, an early Christmas present from the parents.
Of course, iPad mini was sitting on a table near the entrance. I picked up the unit closest to me and started playing around with it. Immediately I noticed how light it was; its thinness came second. Its svelte proportions begged me to fit it in my pocket. Surprisingly, it did! (At least in my ski jacket pocket. It went only halfway into my pants pocket. Clearly I should get real cargo pants.)
I then investigated its usability. Upon waking the device, I noticed the blurriness of the clock and app names. Icons were smaller, but still plenty touchable. I then pulled up some scientific papers, but the unfortunate combinations of large margins and smaller and blurrier text heavily outweighed the size and weight of the device. Although I was decided on the iPad 4 at this point, I did my handwriting and typing tests for sake of completeness: I opened up the Paper app and started writing. While a 4:3 ratio is optimal for these smaller devices, 7.9" diagonal does not provide sufficient surface area for writing notes without constantly flipping pages. Yes, I do handwrite my notes on iPad with a stylus, and it works remarkably well. The typing test went surprisingly well; while the keys are considerably more cramped than those of the iPad 4, I was able to type surprisingly quickly (~50wpm).
My impression of iPad 4 is more positive. The retina display is absolutely gorgeous. Also noticeable is the increased weight from iPad 2; while it is heavier, it will be lying on a flat surface most of the time for writing notes. The device does get warm under heavy use (games), in particular, like the iPad 3, the bottom left gets noticeably warm. Perhaps the best change is the speakers (yes, there are two speakers behind the grill); they are significantly louder, maybe on par with those in MacBooks.
The iPod touch is pretty nice, but the iPad nano was pretty bleh. What in the world was Jony Ive thinking?! I'm slightly convinced that it was designed by the marketing team. Ha.
That's all for now; I'll report back if I notice more worthwhile tidbits.