In fact, the response to KDE 4 was quite similar.

The problem with KDE 4.0 was that it was simply nowhere near release quality; huge chunks of it were either massively buggy or simply not implemented, and it took them until 4.3 to get it to a state that I was prepared to use it as my desktop. At that point it worked pretty much identically to KDE 3.x, even though the underlying code had been completely rewritten, and I could just ignore the new stuff I had no use for such as activities without it affecting my desktop experience at all.

Unity, while it's less ugly than GNOME 3 and not quite as awful, still shares many of the same fundamental design flaws. No amount of bug fixing and tweaks can make a desktop usable when the basic ideas behind it are so wrong.

What concerns me in particular, is that at least with the KDE 4.0 debacle, there were quite a few "This is BAD... But I can see it being good in a few versions" type comments.... with Gnome 3, can't think I've seen a single positive comment, at best "changes are sorta manageable".

Yup. The problem with KDE 4.0 was that it simply wasn't even close to release quality; it was early alpha at best, with large chunks of functionality either buggy or unimplemented. 4.2.2 was the first version that I could imagine anyone using as their default desktop; I switched somewhere in the 4.3.x sequence.

The problem with GNOME 3 is that the fundamental design decisions are wrong. No amount of bug fixing etc. is going to make it usable.

I've just tried this. The most obvious change is the new 'K' menu, which is unbelievably
awful and difficult to use. If there's no way to turn this junk off and go back to a
sane way of doing things then that alone will be enough to keep me on KDE 3.x. The system settings window is also horribly broken - the nice tree view of all the sections has been replaced with a stupid layout that requires me to constantly click on the back button when I'm looking for something.

Does anyone know if the changes will prevent old themes from working? I like the Marble theme from old versions of KDE and have been adding it back myself since they inexplicably dropped it. Assuming they fix the thingsI mentioned above and I switch to 4.x, I'd like to be able to use it.