A few years ago I got excited about the prospects of a Next-Gen Amiga OS. I followed the news on OS 4, picked up an A4000 (I had never personally owned an Amiga until that point, though my grandfather did) and messed around with AROS a bit. I was dissatisfied with the more mainstream OS options and wanted to try something different.
After a while I came to the conclusion that while Amiga OS was quite advanced for its time, it's time had passed. The design of the OS itself is dated and so is most of the software. Certainly some of the user experience is worth saving (fast boot times, actual simplicity rather than a simple veneer on top of an overly complex infrastructure like Linux or OS X, etc.), but you have to wonder whether dragging the Amiga's rotting carcass into modern computing is really the best solution.
There are other alternative operating systems that achieve at least some parts of the Amiga user experience. I've grown quite fond of Syllable. It's not quite to the point where it can replace Windows as my primary OS, but it's a lot closer to achieving that than my A4000 or AROS. Haiku an open source BeOS clone) is also an option though not quite as far along as Syllable in many regards.
I am quite interested in the Minimig/CloneA, but not as a desktop platform