I can vouch that MorphOS is good enough to use and not wish you had OS4 instead. I have no plans to ever get an OS4 system so long as they are priced the way they were the last time you could get one.
MorphOS does everything it can do, and I would say just as well if not better in areas too.
As a counter to that, I should point out that, having both MOS and OS4, I haven't switched on my Peg for about 3 months (although I intend to tonight) due mainly to my impression that OS4 actually does most things more elegantly, although I admit this is subjective.
That said, I tend to do most of my work in OSX these days.
