MorphOS is pretty cool, very fast and stable (for an amiga type OS). If you consider it a hobby, "novelty" type thing it can be quite a bit of fun to play with, and you can make it look beautiful using MUI. (For an example, you can see my old ambient screenshots
here at Morphzone.:-P :-))
On the downside...MorphOS is not going to be nearly as stable as MacOS (though it's not intended to be at this point), and necessary applications (like modern web browsers) do not exist, not to mention things like new commercial games/etc. Linux works well on the Pegasos (minus some glitches with 3d acceleration, at least back when I installed Debian) but I would not even consider buying one if you're mainly going to be running linux...a PC would be much better suited for that task not to mention cheaper and more powerful.
Bottom line IMHO...is that if you're looking for a something to replace your everyday machine, get a Mac...or a PC and run WinUAE. On the other hand, the Pegasos makes a solid choice for a secondary fun/hobby setup...you would likely enjoy owning it, but it's expensive and not very practical.
Sometimes I miss mine, if I had the cash to burn and the time to play I would consider buying another.