Hey Akira... the sun's dissapeared!!!!
I beleive that most of the criticisms levelled at MUI have been that lower end Amigas have never really had the memory or processor resources to run it at it's optimum. I know that 'lots' of people have 040/060 machines, some have PPC, but compared to the majority of the user base... it's a small percentage who have "fast" Amigas. Personally I don't use MUI. The Amiga's interface isn't that pretty compared to some, but it works well enough, and any programmer can code for the standard interface.
Pyro has a point about MUI running on G3 or G4 machines. Fine... Windoze XP runs fine on my AMD XP 2000+, but if you have a P3 500... it ain't so hot. The next generation of MUI may run well on modern hardware, but that's assuming you have hardware in the first place. How many people actually own a Pegasos PC or an Amiga One? Hundreds? Maybe a couple of thousand worldwide? In the meantime, think of all th 030 units out there, simply because anything more cost an arm and a leg.
Anyway, it's all about choice. Use what you wish as long as YOU are happy with it.
End of sermon!
Today I took delvery of an A1200 complete with 040/33 with one of those enhanced IDE interfaces... can't wait to get her home and put her through her paces.